Method and apparatus for transmitting and receiving data in wireless communication system

ABSTRACT

Provided is a method of performing a random access procedure, the method including: selecting, from among a plurality of Synchronization Signal Blocks (SSBs), a first SSB that exceeds a threshold value of signal power; transmitting a contention-based random access preamble corresponding to the first SSB; receiving a first Random Access Response (RAR) corresponding to the contention-based random access preamble; obtaining a first Media Access Control Protocol Data Unit (MAC PDU) corresponding to a size of uplink (UL) resource allocation in the first RAR; transmitting a message3 (Msg3) including the first MAC PDU; determining, by transmitting the Msg3, whether contention is resolved; and when the contention is not resolved, performing a contention-free random access procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage of International ApplicationNo. PCT/KR2019/007891, filed Jun. 28, 2019, which claims priority toKorean Patent Application No. 10-2018-0075593, filed Jun. 29, 2018, thedisclosures of which are herein incorporated by reference in theirentirety.

BACKGROUND 1. Field

The disclosure relates to a method and apparatus for transmitting andreceiving data in a wireless communication system.

2. DESCRIPTION OF RELATED ART

To meet increasing demand with respect to wireless data traffic afterthe commercialization of 4^(th) generation (4G) communication systems,efforts have been made to develop evolved 5^(th) generation (5G) systemor pre-5G communication system. For this reason, 5G or pre-5Gcommunication systems are called ‘beyond 4G network’ communicationsystems or ‘post long term evolution (post-LTE)’ systems. To achievehigh data rates, implementation of 5G communication systems in anultra-high frequency or millimeter-wave (mmWave) band (e.g., a 60 GHzband) is being considered. To reduce path loss of radio waves andincrease a transmission distance of radio waves in the ultra-highfrequency band for 5G communication systems, various technologies suchas beamforming, massive multiple-input and multiple-output (massiveMIMO), full-dimension MIMO (FD-MIMO), array antennas, analogbeamforming, and large-scale antennas are being studied. To improvesystem networks for 5G communication systems, various technologies suchas evolved small cells, advanced small cells, cloud Radio AccessNetworks (Cloud-RAN), ultra-dense networks, Device-To-Devicecommunication (D2D), wireless backhaul, moving networks, cooperativecommunication, Coordinated Multi-Points (CoMP), interferencecancellation, or the like have been developed. In addition, for 5Gcommunication systems, advanced coding modulation (ACM) technologiessuch as hybrid frequency-shift keying (FSK) and quadrature amplitudemodulation (QAM) (FQAM) and sliding window superposition coding (SWSC),and advanced access technologies such as filter bank multi-carrier(FBMC), non-orthogonal multiple access (NOMA), sparse code multipleaccess (SCMA), or the like have been developed.

The Internet has evolved from a human-based connection network, wherehumans create and consume information, to the Internet of things (IoT),where distributed elements such as objects exchange information witheach other to process the information. Internet of everything (IoE)technology has emerged, in which the IoT technology is combined with,for example, technology for processing big data through connection witha cloud server. To implement the IoT, various technological elementssuch as sensing technology, wired/wireless communication and networkinfrastructures, service interface technology, and security technologyare required, such that, in recent years, technologies related to sensornetworks for connecting objects, Machine-To-Machine (M2M) communication,and Machine-Type Communication (MTC) have been studied. In the IoTenvironment, intelligent Internet technology (IT) services may beprovided to collect and analyze data obtained from connected objects tocreate new value in human life. As existing information technology (IT)and various industries converge and combine with each other, the IoT maybe applied to various fields such as smart homes, smart buildings, smartcities, smart cars or connected cars, smart grids, health care, smarthome appliances, and advanced medical services.

Various attempts are being made to apply 5G communication systems to theIoT network. For example, 5G communication technologies such as sensornetworks, M2M communication, MTC, or the like are being implemented byusing techniques including beamforming, MIMO, array antennas, or thelike. Application of Cloud-RAN as the above-described big dataprocessing technology may be an example of convergence of 5Gcommunication technology and IoT technology.

Because various services may be provided due to the aforementionedtechnical features and the development of wireless communicationsystems, methods for effectively providing these services are required.

SUMMARY

Disclosed embodiments provide an apparatus and method for effectivelyproviding a service in a mobile communication system.

Disclosed embodiments provide an apparatus and method for effectivelyproviding a service in a mobile communication system.

Disclosed embodiments can effectively provide a service in a mobilecommunication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating a configuration of a long termevolution (LTE) system, according to some embodiments of the disclosure.

FIG. 1B is a diagram illustrating a radio protocol architecture of anLTE system, according to some embodiments of the disclosure.

FIG. 1C is a diagram illustrating an architecture of a next-generationmobile communication system, according to some embodiments of thedisclosure.

FIG. 1D is a diagram illustrating a radio protocol architecture of anext-generation mobile communication system, according to an embodimentof the disclosure.

FIG. 1E is a diagram illustrating a procedure in which a user equipment(UE) performs Radio Resource Control (RRC) connection configuration witha base station (BS) when the UE configures connection to a network in awireless communication system, according to some embodiments of thedisclosure.

FIG. 1F is a diagram illustrating a procedure in which packetduplication transmission is configured and is performed in an activestate and an inactive state in a next-generation mobile communicationsystem, according to some embodiments of the disclosure.

FIG. 1G is a diagram for describing operations of a UE according to someembodiments of the disclosure.

FIG. 1H illustrates a configuration of a UE according to someembodiments of the disclosure.

FIG. 1I is a block diagram of a transmission/reception point (TRP) in awireless communication system, according to some embodiments of thedisclosure.

FIG. 2A is a diagram illustrating a configuration of an LTE system,according to some embodiments of the disclosure.

FIG. 2B illustrates radio protocol architectures of an LTE system and anew radio (NR) system to be referenced for descriptions of thedisclosure.

FIG. 2C illustrates downlink (DL) and uplink (UL) channel framestructures when a beam-based communication is performed in an NR system,according to some embodiments of the disclosure.

FIG. 2D illustrates contention and contention-free random accessprocedures performed in a situation such as handover by a UE to a BS,according to some embodiments of the disclosure.

FIG. 2E is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 1 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2F is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 2 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2G is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 3 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2H is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 4 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2I is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 5 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2J is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 6 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure.

FIG. 2K illustrates a configuration of a UE in a wireless communicationsystem according to some embodiments of the disclosure.

DETAILED DESCRIPTION

According to an embodiment of the disclosure, a method of performing arandom access procedure, the method being performed by a user equipment(UE), includes: selecting, from among a plurality of SynchronizationSignal Blocks (SSBs), a first SSB that exceeds a threshold value ofsignal power; transmitting a contention-based random access preamblecorresponding to the first SSB; receiving a first Random Access Response(RAR) corresponding to the contention-based random access preamble;obtaining a first Media Access Control Protocol Data Unit (MAC PDU)corresponding to a size of uplink (UL) resource allocation in the firstRAR;

transmitting a message3 (Msg3) including the first MAC PDU; determining,by transmitting the Msg3, whether contention is resolved; and when thecontention is not resolved, performing a contention-free random accessprocedure.

The first MAC PDU may be obtained from a multiplexing and assemblyentity.

The first MAC PDU may include a Cell-Radio Network Temporary IdentifierMedia Access Control Control Element (C-RNTI MAC CE).

The method may further include storing the first MAC PDU in an Msg3buffer.

The performing of the contention-free random access procedure mayinclude: selecting a second SSB exceeding the threshold value of thesignal power, from among a plurality of SSBs to which contention-freerandom access preambles are allocated; transmitting a contention-freerandom access preamble corresponding to the second SSB; receiving asecond RAR corresponding to the contention-free random access preamble;obtaining the first MAC PDU; obtaining a second MAC PDU, based on thefirst MAC PDU; and transmitting the second MAC PDU.

The obtaining of the first MAC PDU may include: determining whether thefirst MAC PDU is stored in an Msg3 buffer; and based on a result of thedetermining, obtaining the first MAC PDU from the Msg3 buffer.

The obtaining of the second MAC PDU based on the first MAC PDU mayinclude: comparing a size of UL resource allocation in the second RARwith a size of the first MAC PDU; and based on a result of thecomparing, obtaining the second MAC PDU to include, in subsequent ULtransmission, at least one MAC subProtocol Data Unit (MAC subPDU) in thefirst MAC PDU.

The second MAC PDU may be obtained from a multiplexing and assemblyentity.

The method may further include deleting data in the Msg3 buffer.

The determining of whether the contention is resolved may includedetermining whether a response to the Msg3 is received until ara-ContentionResolution timer is expired.

According to an embodiment of the disclosure, a user equipment (UE)performing a random access procedure includes: a transceiver; and atleast one controller coupled with the transceiver and configured toselect, from among a plurality of Synchronization Signal Blocks (SSBs),a first SSB that exceeds a threshold value of signal power, transmit acontention-based random access preamble corresponding to the first SSB,receive a first Random Access Response (RAR) corresponding to thecontention-based random access preamble, obtain a first Media AccessControl Protocol Data Unit (MAC PDU) corresponding to a size of uplink(UL) resource allocation in the first RAR, transmit a message3 (Msg3)including the first MAC PDU, determine, by transmitting the Msg3,whether contention is resolved, and when the contention is not resolved,perform a contention-free random access procedure.

The at least one controller may be further configured to select a secondSSB exceeding the threshold value of the signal power, from among aplurality of SSBs to which contention-free random access preambles areallocated, transmit a contention-free random access preamblecorresponding to the second SSB, receive a second RAR corresponding tothe contention-free random access preamble, obtain the first MAC PDU,obtain a second MAC PDU, based on the first MAC PDU, and transmit thesecond MAC PDU.

The at least one controller may be further configured to determinewhether the first MAC PDU is stored in an Msg3 buffer, and based on aresult of the determining, obtain the first MAC PDU from the Msg3buffer.

The at least one controller may be further configured to compare a sizeof UL resource allocation in the second RAR with a size of the first MACPDU, and based on a result of the comparing, obtain the second MAC PDUto include, in subsequent UL transmission, at least one MAC subProtocolData Unit (MAC subPDU) in the first MAC PDU.

The second MAC PDU may be obtained from a multiplexing and assemblyentity.

Hereinafter, operation principles of the disclosure will be described indetail with reference to accompanying drawings. In the followingdescriptions of the disclosure, well-known functions or configurationsare not described in detail because they would obscure the disclosurewith unnecessary details. The terms used in the specification aredefined in consideration of functions used in the disclosure, and can bechanged according to the intent or commonly used methods of users oroperators. Accordingly, definitions of the terms are understood based onthe entire descriptions of the present specification.

For the same reason, some elements in the drawings are exaggerated,omitted, or schematically illustrated. Also, the size of each elementdoes not entirely reflect the actual size. In the drawings, the same orcorresponding elements are denoted by the same reference numerals.

The advantages and features of the disclosure and methods of achievingthem will become apparent with reference to embodiments described indetail below with reference to the accompanying drawings. The disclosuremay, however, be embodied in many different forms and should not beconstrued as limited to embodiments set forth herein; rather theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure only definedby the claims to one of ordinary skill in the art. Throughout thespecification, like reference numerals refer to like elements.

It will be understood that each block of flowchart illustrations, andcombinations of blocks in the flowchart illustrations, may beimplemented by computer program instructions. The computer programinstructions may be provided to a processor of a general-purposecomputer, special purpose computer, or other programmable dataprocessing apparatus, such that the instructions, which are executed viathe processor of the computer or other programmable data processingapparatus, generate means for performing functions specified in theflowchart block or blocks. The computer program instructions may also bestored in a computer-executable or computer-readable memory that maydirect the computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-executable or computer-readable memory produce an articleof manufacture including instruction means that perform the functionsspecified in the flowchart block(s). The computer program instructionsmay also be loaded onto the computer or other programmable dataprocessing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions that areexecuted on the computer or other programmable apparatus provide stepsfor implementing the functions specified in the flowchart block(s).

In addition, each block of the flowchart illustrations may represent amodule, segment, or portion of code, which includes one or moreexecutable instructions for performing specified logical function(s). Itshould also be noted that in some alternative implementations, thefunctions noted in the blocks may occur out of the order. For example,two blocks shown in succession may in fact be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

The term “unit”, as used in the present embodiment refers to a softwareor hardware component, such as field-programmable gate array (FPGA) orapplication-specific integrated circuit (ASIC), which performs certaintasks. However, the term “unit” does not mean to be limited to softwareor hardware. A “unit” may be configured to be in an addressable storagemedium or configured to operate one or more processors. Thus, a “unit”may include, by way of example, components, such as software components,object-oriented software components, class components, and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided in the components and “units” may be combinedinto fewer components and “units” or may be further separated intoadditional components and “units”. Further, the components and “units”may be implemented to operate one or more central processing units(CPUs) in a device or a secure multimedia card. Also, a “unit” mayinclude one or more processors in embodiments.

In the following descriptions of the disclosure, well-known functions orconfigurations are not described in detail because they would obscurethe disclosure with unnecessary details. Hereinafter, embodiments of thedisclosure will be described in detail with reference to accompanyingdrawings.

Hereinafter, terms identifying an access node, terms indicating networkentities, terms indicating messages, terms indicating an interfacebetween network entities, and terms indicating various pieces ofidentification information, as used in the following description, areexemplified for convenience of explanation. Accordingly, the disclosureis not limited to terms to be described below, and other termsindicating objects having equal technical meanings may be used.

For convenience of descriptions, the disclosure uses terms and namesdefined in the 3rd Generation Partnership Project (3GPP) long termevolution (LTE) standards. However, the disclosure is not limited tothese terms and names, and may be equally applied to communicationsystems conforming to other standards. In the disclosure, an evolvednode B (eNB) may be interchangeably used with a next-generation node B(gNB) for convenience of explanation. That is, a base station describedby an eNB may represent a gNB. In the disclosure, the term “terminals”may refer to not only mobile phones, narrowband IoT (NB-IoT) devices,and sensors but also other wireless communication devices. In thefollowing description, the term “base station” refers to an entity forallocating resources to a user equipment and may be used interchangeablywith at least one of a gNode B, an eNode B, a node B, a base station(BS), a radio access unit, a base station controller (BSC), or a nodeover a network The term “terminal” may be used interchangeably with auser equipment (UE), a mobile station (MS), a cellular phone, asmartphone, a computer, or a multimedia system capable of performingcommunication functions. However, the disclosure is not limited to theaforementioned examples.

In particular, the disclosure may be applied to 3GPP New Radio (NR) (5Gmobile communication standard). The disclosure is applicable tointelligent services (e.g., smart home, smart building, smart city,smart car or connected car, health care, digital education, retail,security, and safety services) based on 5G communication technology andInternet of things (IoT) technology. In the disclosure, an eNB may beinterchangeably used with a gNB for convenience of explanation. That is,a BS described by an eNB may represent a gNB. In the disclosure, theterm “terminals (UEs)” may refer to not only mobile phones, NB-IoTdevices, and sensors but also other wireless communication devices.

Wireless communication systems have been developed from wirelesscommunication systems providing voice centered services in the earlystage toward broadband wireless communication systems providinghigh-speed, high-quality packet data services, like communicationstandards of high speed packet access (HSPA), long term evolution (LTEor evolved universal terrestrial radio access (E-UTRA)), LTE-Advanced(LTE-A), and LTE-Pro of the 3GPP, high rate packet data (HRPD) and ultramobile broadband (UMB) of 3GPP2, 802.16e of the Institute of Electricaland Electronic Engineers (IEEE), or the like.

As a representative example of the broadband wireless communicationsystem, the LTE system has adopted an orthogonal frequency divisionmultiplexing (OFDM) scheme in a downlink (DL) and has adopted a singlecarrier frequency division multiple access (SC-FDMA) scheme in an UL.The UL refers to a radio link through which a UE (also referred to as amobile station (MS)) transmits data or a control signal to a BS (e.g.,eNB), and the DL refers to a radio link through which a BS transmitsdata or a control signal to a UE. The above-described multiconnectionscheme distinguishes between data or control information of differentusers by assigning time-frequency resources for the data or controlinformation of the users not to overlap each other, i.e., to achieveorthogonality therebetween.

Post-LTE systems, that is, 5G systems need to simultaneously supportservices capable of reflecting and satisfying various requirements ofusers, service providers, etc. Services considered for the 5G systemsinclude enhanced mobile broadband (eMBB), massive machine-typecommunication (mMTC), ultra-reliability low-latency communication(URLLC) services or the like.

According to some embodiments, the eMBB service may be aimed to providea more enhanced data rate compared to a data rate supported by LTE,LTE-A, or LTE-Pro. For example, the eMBB service in the 5G communicationsystems needs to provide a maximum data rate of 20 gigabits per second(Gbps) for a DL and provide a maximum data rate of 10 Gbps for a UL inview of a single BS. At the same time, the 5G communication systems maysimultaneously provide a maximum data rate and provide an increased userperceived data rate. To satisfy these requirements, the 5G communicationsystems may require various enhanced transmission/reception technologiesincluding enhanced multiple-input and multiple-output (MIMO). The datarate required for the 5G communication systems may be satisfied by usinga frequency bandwidth wider than 20 megahertz (MHz) in a frequency bandof 3 to 6 GHz or over 6 GHz compared to LTE systems currently using atransmission bandwidth of up to 20 MHz in a 2 GHz band.

At the same time, the mMTC service is considered for the 5Gcommunication systems to support application services such as IoT. ThemMTC service may be required to, for example, support massive useraccess within a cell, enhance UE coverage, increase battery time, andreduce user charges, to efficiently provide the IoT service. The IoTservice provides a communication function by using a variety of sensorsattached to various devices, and thus needs to support a large number ofUEs within a cell (e.g., 1,000,000 UEs/km2. In addition, because UEssupporting mMTC may be located in a shadow zone, e.g., a basement of abuilding, due to service characteristics, the mMTC service may require awider coverage compared to other services provided by the 5Gcommunication systems. The UEs supporting mMTC need to be low-priced,and are not able to frequently replace batteries and thus require a verylong battery life time, e.g., 10 to 15 years.

Lastly, the URLLC service is a mission-critical cellular-based wirelesscommunication service and may be used for remote control of robots ormachinery, industrial automation, unmanned aerial vehicles, remotehealthcare, emergency alert, etc. Thus, URLLC communication may have toprovide a very low latency (e.g., ultra-low latency) and a very highreliability (e.g., ultra-reliability). For example, the URLLC serviceneeds to satisfy an air interface latency smaller than 0.5 millisecond(ms) and, at the same time, may require a packet error rate equal to orsmaller than 10⁻⁵. Therefore, for the URLLC service, the 5Gcommunication systems need to provide a smaller transmit time interval(TTI) compared to other services and, at the same time, may be requiredto broadly allocate resources in a frequency band to ensure reliabilityof a communication link.

The above-described three services considered for the 5G communicationsystems, i.e., the eMBB, URLLC, and mMTC services, may be multiplexedand provided by a single system. In this case, the services may usedifferent transmission/reception schemes and differenttransmission/reception parameters to satisfy different requirements forthe services. The above-described mMTC, URLLC, and eMBB services aremerely examples and the types of services to which the disclosure isapplicable are not limited thereto.

Although LTE, LTE-A, LTE Pro, or 5G (or NR) systems are mentioned asexamples in the following description, embodiments of the disclosure mayalso be applied to other communication systems having similar technicalbackgrounds or channel types. Furthermore, the embodiments of thedisclosure may also be applied to other communication systems throughpartial modification without greatly departing from the scope of thedisclosure based on determination by one of ordinary skill in the art.

In the disclosure, provided are a method and apparatus for efficientlysupporting a Secondary Cell (Scell) Radio Link Failure (RLF) in anext-generation mobile communication system, and a method by which aconnected-UE can generate and transmit a message3 (Msg3) when theconnected-UE performs a random access.

In the wireless communication system, in order to support lowertransmission latency and guarantee higher reliability, packetduplication transmission may be applied to and used for a UL and a DL.According to the packet duplication transmission, a same packet isduplicately transmitted through two Radio Link Control (RLC) entities,and when a retransmission count with respect to certain data exceeds inone of the two RLC entities which is connected to a Scell, the one RLCentity declares a Scell RLF. That is, a UE may report, to a BS by usinga Radio Resource Control (RRC) message, that a maximum retransmissioncount with respect to certain data exceeds in the RLC entity connectedto the Scell, and this may be referred to as the Scell RLF. According tosome embodiments of the disclosure, during a procedure of triggering andtransmitting a Scell RLF, provided is a method of preventing the ScellRLF from being unnecessarily triggered several times, and efficientlymanaging parameters for calculating a maximum retransmission count.

Also, according to an embodiment of the disclosure, provided is a methodby which a BS receives detailed information about a most recentsuccessful random access of a UE from each of UEs so as to efficientlyallocate random access channels (e.g., the number of random accesschannels, etc.,) to the UEs within a cell.

FIG. 1A is a diagram illustrating a configuration of an LTE system,according to some embodiments of the disclosure.

Referring to FIG. 1A, a radio access network (RAN) of the LTE systemincludes a plurality of eNBs (or nodes B or BSs) 1 a-05, 1 a-10, 1 a-15,and 1 a-20, a mobility management entity (MME) 1 a-25, and aserving-gateway (S-GW) 1 a-30. A UE (or a terminal) 1 a-35 may access anexternal network via the eNB 1 a-05, 1 a-10, 1 a-15, or 1 a-20 and theS-GW 1 a-30.

In FIG. 1A, the eNB 1 a-05, 1 a-10, 1 a-15, or 1 a-20 may correspond toan existing node B of a universal mobile telecommunications system(UMTS). The eNB may be connected to the UE 1 a-35 through wirelesschannels and may perform complex functions compared to the existing nodeB. All user traffic data including real-time services such as voice overInternet protocol (VoIP) may be serviced through shared channels in theLTE system, and thus an entity for collating status information, e.g.,buffer status information, available transmission power statusinformation, and channel state information, of UEs and performingscheduling may be required and the eNB 1 a-05, 1 a-10, 1 a-15, or 1 a-20may operate as such an entity. One eNB generally controls a plurality ofcells. For example, the LTE system may use radio access technology suchas OFDM at a bandwidth of 20 MHz to achieve a data rate of 100 Mbps.Furthermore, the eNB may also use adaptive modulation & coding (AMC) todetermine a modulation scheme and a channel coding rate in accordancewith a channel state of the UE. The S-GW 1 a-30 is an entity forproviding data bearers and may establish and release the data bearers bythe control of the MME 1 a-25. The MME is an entity for performing amobility management function and various control functions on the UE andis connected to the plurality of eNBs.

FIG. 1B is a diagram illustrating a radio protocol architecture of anLTE system, according to some embodiments of the disclosure.

Referring to FIG. 1B, radio protocols of the LTE system may includePacket Data Convergence Protocol (PDCP) entities 1 b-05 and 1 b-40, RLCentities 1 b-10 and 1 b-35, and Medium Access Control (MAC) entities 1b-15 and 1 b-30 respectively in a UE and an eNB. The PDCP entity 1 b-05or 1 b-40 may perform, for example, IP header compression/decompression.Main functions of the PDCP entity 1 b-05 or 1 b-40 are summarized asshown below. However, the functions thereof are not limited thereto.

-   -   Header compression and decompression: robust header compression        (ROHC) only    -   Transfer of user data    -   In-sequence delivery of upper layer packet data units (PDUs) at        PDCP re-establishment procedure for RLC acknowledged mode (AM)    -   For split bearers in DC (only support for RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception    -   Duplicate detection of lower layer service data units (SDUs) at        PDCP re-establishment procedure for RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

According to some embodiments, the RLC entity 1 b-10 or 1 b-35 mayperform an automatic repeat request (ARQ) operation by reconfiguringPacket Data Convergence Protocol Packet Data Units (PDCP PDUs) toappropriate sizes. Main functions of the RLC entity may be summarized asshown below. However, the functions thereof are not limited thereto.

-   -   Transfer of upper layer PDUs    -   Error correction through ARQ (only for AM data transfer)    -   Concatenation, segmentation and reassembly of RLC SDUs (only for        unacknowledged mode (UM) and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for AM data transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer)    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM data transfer)    -   RLC re-establishment

According to some embodiments, the MAC entity 1 b-15 or 1 b-30 may beconnected to a plurality of RLC entities configured for one UE and maymultiplex RLC PDUs into a MAC PDU and may demultiplex the RLC PDUs fromthe MAC PDU. Main functions of the MAC entity may be summarized as shownbelow. However, the functions thereof are not limited thereto.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TBs)        delivered to/from the physical layer on transport channels    -   Scheduling information reporting    -   Error correction through hybrid ARQ (HARM)    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   Multimedia broadcast/multicast service (MBMS) service        identification    -   Transport format selection    -   Padding

According to some embodiments, a PHY entity 1 b-20 or 1 b-25 maychannel-code and modulate upper layer data into OFDM symbols andtransmit the OFDM symbols through a wireless channel, or may demodulateOFDM symbols received through a wireless channel and channel-decode anddeliver the OFDM symbols to an upper layer. However, the functionsthereof are not limited thereto.

FIG. 1C is a diagram illustrating an applicable architecture of anext-generation mobile communication system, according to someembodiments of the disclosure.

Referring to FIG. 1C, as illustrated, a radio access network of thenext-generation mobile communication system (hereinafter, referred to asthe NR or 5G communication system) includes a new radio node B (NR gNB,NR NB, or gNB) 1 c-10 and a new radio core network (NR CN) 1 c-05. A NRUE (or terminal) 1 c-15 may access an external network via the NR gNB 1c-10 and the NR CN 1 c-05.

In FIG. 1C, the NR gNB 1 c-10 may correspond to an existing eNB of theLTE system. The NR gNB 1 c-10 may be connected to the NR UE 1 c-15through radio channels and may provide superior services compared to anexisting node B. All user traffic data may be serviced through sharedchannels in the NR or 5G mobile communication system, and thus, anentity for collating buffer status information of UEs, availabletransmission power status information, and channel state information andperforming scheduling may be required and the NR gNB 1 c-10 may operateas such an entity. One NR gNB may generally control a plurality ofcells. The next-generation mobile communication system may have abandwidth greater than the maximum bandwidth of the existing LTE systemso as to achieve an ultra-high data rate, compared to the existing LTEsystem, and may use OFDM as a radio access technology and mayadditionally use a beamforming technology.

Also, according to some embodiments, AMC may be used to determine amodulation scheme and a channel coding rate in accordance with a channelstate of the UE. The NR CN 1 c-05 may perform functions such as mobilitysupport, bearer configuration, and quality of service (QoS)configuration. The NR CN 1 c-05 is an entity for performing a mobilitymanagement function and various control functions on the NR UE 1 c-15and may be connected to a plurality of base stations. Thenext-generation mobile communication system may cooperate with theexisting LTE system, and the NR CN 1 c-05 may be connected to an MME 1c-25 through a network interface. The MME 1 c-25 may be connected to aneNB 1 c-30 that is an existing BS.

FIG. 1D is a diagram illustrating a radio protocol architecture of anext-generation mobile communication system, according to an embodimentof the disclosure.

Referring to FIG. 1D, the radio protocol architecture of thenext-generation mobile communication system may include NR Service DataAdaptation Protocol (SDAP) entities 1 d-01 and 1 d-45, NR PDCP entities1 d-05 and 1 d-40, NR RLC entities 1 d-10 and 1 d-35, and NR MACentities 1 d-15 and 1 d-30 respectively for a UE and an NR gNB.

Main functions of the NR SDAP entity 1 d-01 or 1 d-45 may include someof the following functions. However, the functions thereof are notlimited thereto.

-   -   Transfer of user plane data    -   Mapping between a QoS flow and a DRB for both DL and UL    -   Marking QoS flow identifier (ID) in both DL and UL packets    -   Reflective QoS flow to DRB mapping for the UL SDAP PDUs

With regard to a SDAP entity, information about whether to use a headerof the SDAP entity or to use functions of the SDAP entity may beconfigured for the UE by using a RRC message per PDCP entity, perbearer, or per logical channel. Also, when the SDAP header of the SDAPentity is configured, a 1-bit non access stratum (NAS) reflective QoSindicator and a 1-bit access stratum (AS) reflective QoS indicator ofthe SDAP header may indicate the UE to update or reconfigure UL and DLQoS flow and data bearer mapping information. According to someembodiments, the SDAP header may include QoS flow ID informationindicating QoS. Furthermore, according to some embodiments, QoSinformation may be used as data processing priority information orscheduling information for appropriately supporting a service.

According to some embodiments, main functions of the NR PDCP entity 1d-05 or 1 d-40 may include some of the following functions. However, thefunctions thereof are not limited thereto.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs    -   Retransmission of PDCP SDUs    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

According to some embodiments, the reordering function of the NR PDCPentity may include at least one of a function of reordering PDCP PDUsreceived from a lower layer, on a PDCP sequence number (SN) basis, and afunction of delivering the reordered data to an upper layer in order.Alternatively, the reordering function of the NR PDCP entity may includeat least one of a function of delivering the reordered data to an upperlayer out of order, a function of recording missing PDCP PDUs byreordering the received PDCP PDUs, a function of reporting statusinformation of the missing PDCP PDUs to a transmitter, and a function ofrequesting to retransmit the missing PDCP PDUs.

According to some embodiments, main functions of the NR RLC entity 1d-10 or 1 d-35 may include some of the following functions. However, thefunctions thereof are not limited thereto.

-   -   Transfer of upper layer PDUs    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   Error correction through ARQ    -   Concatenation, segmentation and reassembly of RLC SDUs    -   Re-segmentation of RLC data PDUs    -   Reordering of RLC data PDUs    -   Duplicate detection    -   Protocol error detection    -   RLC SDU discard    -   RLC re-establishment

According to some embodiments, the in-sequence delivery function of theNR RLC entity indicates a function of delivering RLC SDUs received froma lower layer to an upper layer in order. The in-sequence deliveryfunction of the NR RLC entity may include at least one of a function ofreassembling the RLC SDUs and delivering the reassembled RLC SDU when aplurality of RLC SDUs segmented from one RLC SDU are received, afunction of reordering received RLC PDUs on an RLC SN or PDCP SN basis,a function of recording missing RLC PDUs by reordering the received RLCPDUs, a function of reporting status information of the missing RLC PDUsto a transmitter, a function of requesting to retransmit the missing RLCPDUs, a function of delivering only RLC SDUs prior to a missing RLC SDU,to an upper layer in order when the missing RLC SDU exists, or afunction of delivering all RLC SDUs received before a timer starts, toan upper layer in order although a missing RLC SDU exists when a certaintimer expires. Furthermore, the out-of-sequence delivery function of theNR RLC entity may process the RLC PDUs in order of reception and deliverthe RLC PDUs to the NR PDCP entity regardless of SNs (out-of-sequencedelivery), and when a received RLC PDU is a segment, the NR RLC entitymay reassemble the segment with other segments stored in a buffer orsubsequently received, into a whole RLC PDU and may transmit the RLC PDUto the NR PDCP entity. According to some embodiments, the NR RLC entitymay not have a concatenation function, and the function may be performedby the NR MAC entity or be replaced with a multiplexing function of theNR MAC entity.

The out-of-sequence delivery function of the NR RLC may include at leastone of a function of directly delivering RLC SDUs received from a lowerlayer to an upper layer out of order, a function of reassembling aplurality of RLC SDUs segmented from one RLC SDU and delivering thereassembled RLC SDU when the segmented RLC SDUs are received, and afunction of recording missing RLC PDUs by storing RLC SNs or PDCP SNs ofreceived RLC PDUs and reordering the received RLC PDUs.

According to some embodiments, the NR MAC entity 1 d-15 or 1 d-30 may beconnected to a plurality of NR RLC entities configured for one UE, andmain functions of the NR MAC entity may include some of the followingfunctions. However, the functions thereof are not limited thereto.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

According to some embodiments, an NR PHY entity 1 d-20 or 1 d-25 maychannel-code and modulate upper layer data into OFDM symbols and maytransmit the OFDM symbols through a wireless channel, or may demodulateOFDM symbols received through a wireless channel and channel-decode andmay deliver the OFDM symbols to an upper layer. However, the functionsthereof are not limited thereto.

FIG. 1E is a diagram illustrating a procedure in which a UE performs RRCconnection configuration with a BS when the UE configures connection toa network in a next-generation mobile communication system, according tosome embodiments of the disclosure.

Referring to FIG. 1E, when the UE configured to transmit or receive datain an RRC connected mode does not transmit or receive data due to apreset reason or during a preset time period, the BS may transmit aRRCConnectionRelease message to the UE so as to indicate the UE toswitch to an RRC idle mode (operation 1 e-01). Afterward, when the UEthat is not currently connected (hereinafter, the idle mode UE) has datato transmit, the UE may perform an RRC connection establishmentprocedure with the BS.

The UE establishes inverse direction transmission synchronization withthe BS via a random access procedure, and transmits anRRCConnectionRequest message to the BS (operation 1 e-05). TheRRCConnectionRequest message may include an identifier of the UE, anestablishment cause, or the like.

The BS transmits an RRCConnectionSetup message to indicate the UE toestablish RRC connection (operation 1 e-10). The RRCConnectionSetupmessage may include at least one of configuration information of eachlogical channel, configuration information of each bearer, PDCP entityconfiguration information, RLC entity configuration information, and MACentity configuration information.

Also, the BS may configure dual connectivity and carrier aggregation tothe UE by configuring, in the RRCConnectionSetup message, the PDCPentity configuration information, a bearer identifier, a logical channelidentifier, information of mapping between a logical channel and a cell(frequency), cell group configuration information, or a threshold valueto be used in the dual connectivity.

Furthermore, according to some embodiments, in order to configure the UEwith UL or DL packet duplication transmission in the RRCConnectionSetupmessage, two RLC entities may be configured in the PDCP entityconfiguration information, and a primary RLC entity and a secondary RLCentity may be indicated by using logical channel identifiers orindicators. In the descriptions above, packet duplication transmissionmay be used in both the dual connectivity and the carrier aggregation.

Furthermore, according to some embodiments, the RRCConnectionSetupmessage may configure an initial state of a bearer (e.g., a SignalingRadio Bearer (SRB) or a Data Radio Bearer (DRB)) configured with thepacket duplication transmission to an active state or an inactive state.Also, a mapping relation between respective RLC entities and cells maybe configured in the RRCConnectionSetup message. For example, theRRCConnectionSetup message may configure the primary RLC entity to beconnected or mapped to a primary cell (Pcell), and configure thesecondary RLC entity to be connected or mapped to a Secondary cell 1(Scell 1) or Scell 2.

According to some embodiments, an RLC entity for which mapping with acell is configured may transmit data only to the mapped cell. Also, inthe RRCConnectionSetup message, information of mapping between QoS flowsand bearers may be configured through the SDAP entity configurationinformation or the PDCP entity configuration information, and the SDAPentity may transmit data to the PDCP entity configured due to mapping,the data being received from an upper layer by using the mappinginformation. Furthermore, the RRCConnectionSetup message may indicate aretransmission count that is maximally allowed in an RLC entityoperating in an Acknowledged Mode (AM). Also, the RRCConnectionSetupmessage may include RRC connection configuration information, or thelike. RRC connection refers to an SRB, and may be used in transmissionor reception of an RRC message that is a control message between the UEand the BS.

The UE that set up the RRC connection transmits anRRCConnetionSetupComplete message to the BS (operation 1 e-15). TheRRCConnetionSetupComplete message may include a control message ofSERVICE REQUEST requesting, by the UE, an Access and Mobility Function(AMF) or an MME for a bearer configuration for a preset service. The BSmay transmit the SERVICE REQUEST message included in theRRCConnetionSetupComplete message to the AMF or the MME (operation 1e-20). The AMF or the MME may determine whether to provide the servicerequested by the UE.

As a result of the determination, when the AMF or the MME determines toprovide the service requested by the UE, the AMF or the MME transmits anINITIAL CONTEXT SETUP REQUEST message to the BS (operation 1 e-25). TheINITIAL CONTEXT SETUP REQUEST message may include QoS information to beapplied to a configuration of a DRB, security information (e.g., asecurity key, a security algorithm, or the like) to be applied to theDRB, or the like.

The BS transmits and receives a SecurityModeCommand message (operation 1e-30) and a SecurityModeComplete message (operation 1 e-35) to and fromthe UE so as to configure security. When the configuration of thesecurity is completed, the BS transmits an RRCConnectionReconfigurationmessage to the UE (operation 1 e-40).

The RRCConnectionReconfiguration message may include at least one ofconfiguration information of each logical channel, configurationinformation of each bearer, PDCP entity configuration information, RLCentity configuration information, and MAC entity configurationinformation. Also, the BS may configure dual connectivity and carrieraggregation to the UE by configuring, in theRRCConnectionReconfiguration message, the PDCP entity configurationinformation, a bearer identifier, a logical channel identifier,information of mapping between a logical channel and a cell (frequency),cell group configuration information, or a threshold value to be used inthe dual connectivity.

Furthermore, in order to configure the UE with UL or DL packetduplication transmission in the RRCConnectionReconfiguration message,two RLC entities may be configured in the PDCP entity configurationinformation, and a primary RLC entity and a secondary RLC entity may beindicated by using logical channel identifiers or indicators.

According to some embodiments, packet duplication transmission may beused in both the dual connectivity and the carrier aggregation.Furthermore, the RRCConnectionReconfiguration message may configure aninitial state of a bearer (e.g., a SRB or a DRB) configured with thepacket duplication transmission to an active state or an inactive state.Also, a mapping relation between respective RLC entities and cells maybe configured in the RRCConnectionReconfiguration message, and forexample, the RRCConnectionReconfiguration message may configure theprimary RLC entity to be connected or mapped to a primary cell (Pcell),and configure the secondary RLC entity to be connected or mapped to aSecondary cell 1 (Scell 1) or Scell 2 According to some embodiments, anRLC entity for which mapping with a cell is configured may transmit dataonly to the mapped cell.

Also, in the RRCConnectionReconfiguration message, information ofmapping between QoS flows and bearers may be configured through the SDAPentity configuration information or the PDCP entity configurationinformation, and the SDAP entity may transmit data to the PDCP entityconfigured due to mapping, the data being received from an upper layerby using the mapping information. Furthermore, theRRCConnectionReconfiguration message may indicate a retransmission countthat is maximally allowed in an RLC entity operating in an AM. TheRRCConnectionReconfiguration message may include configurationinformation about a DRB in which user data is to be processed, and theUE may configure the DRB by using the information and may transmit anRRCConnectionReconfigurationComplete message to the BS (operation 1e-45). After the BS completes the configuration of the DRB for the UE,the BS may transmit an INITIAL CONTEXT SETUP COMPLETE message to the AMFor the MME and may complete connection (operation 1 e-50).

When the procedure is completed, the UE transmits or receives data to orfrom the BS via a core network (operations 1 e-55 and 1 e-60). Accordingto some embodiments, a data transmission procedure is broadly composedof three operations that are RRC connection setup, securityconfiguration, and DRB configuration. Also, the BS may transmit an RRCConnection Reconfiguration message to newly perform or add configurationfor the UE due to preset reasons (operation 1 e-65). TheRRCConnectionReconfiguration message may include at least one ofconfiguration information of each logical channel, configurationinformation of each bearer, PDCP entity configuration information, RLCentity configuration information, and MAC entity configurationinformation. Also, the BS may configure dual connectivity and carrieraggregation to the UE by configuring, in theRRCConnectionReconfiguration message, the PDCP entity configurationinformation, a bearer identifier, a logical channel identifier,information of mapping between a logical channel and a cell (frequency),cell group configuration information, or a threshold value to be used inthe dual connectivity. Furthermore, in order to configure the UE with ULor DL packet duplication transmission in theRRCConnectionReconfiguration message, two RLC entities may be configuredin the PDCP entity configuration information, and a primary RLC entityand a secondary RLC entity may be indicated by using logical channelidentifiers or indicators. According to some embodiments, packetduplication transmission may be used in both the dual connectivity andthe carrier aggregation.

Furthermore, the RRCConnectionReconfiguration message may configure aninitial state of a bearer (e.g., a SRB or a DRB) configured with thepacket duplication transmission to an active state or an inactive state.Also, a mapping relation between respective RLC entities and cells maybe configured in the RRCConnectionReconfiguration message, and forexample, the RRCConnectionReconfiguration message may configure theprimary RLC entity to be connected or mapped to a primary cell (Pcell),and configure the secondary RLC entity to be connected or mapped to aSecondary cell 1 (Scell 1) or Scell 2 According to some embodiments, anRLC entity for which mapping with a cell is configured may transmit dataonly to the mapped cell. However, the disclosure is not limited thereto.Also, in the RRCConnectionReconfiguration message, information ofmapping between QoS flows and bearers may be configured through the SDAPentity configuration information or the PDCP entity configurationinformation, and the SDAP entity may transmit data to the PDCP entityconfigured due to mapping, the data being received from an upper layerby using the mapping information. Furthermore, theRRCConnectionReconfiguration message may indicate a retransmission countthat is maximally allowed in an RLC entity operating in an AM.

FIG. 1F is a diagram illustrating a procedure in which packetduplication transmission is configured and is performed in an activestate and an inactive state in a next-generation mobile communicationsystem, according to some embodiments of the disclosure.

According to some embodiments, when the UE receives configuration of thepacket duplication transmission from the BS through an RRC message asdescribed with reference to FIG. 1E, the UE may configure the packetduplication transmission. When the packet duplication transmissionconfigured through the RRC message is configured in Carrier Aggregation(CA), the UE may configure two RLC entities, i.e., a primary RLC entity1 f-16 and a secondary RLC entity 1 f-10, for a bearer or a PDCP entityto which the packet duplication transmission is configured. In a casewhere the packet duplication transmission is inactivated, when the PDCPentity transmits a packet to a lower RLC entity in UL transmission, thePDCP entity transmits the packet only to a primary RLC entity and doesnot transmit the packet to a secondary RLC entity. In a case where thepacket duplication transmission is activated, in UL transmission, thePDCP entity may duplicately transmit a same packet to each of two lowerRLC entities (the primary RLC entity and the secondary RLC entity). Thatis, the PDCP entity may transmit a packet to the primary RLC entity, andmay duplicate the packet and thus may transmit the same packet to thesecondary RLC entity.

When the packet duplication transmission is configured and activated inthe CA, a MAC entity 1 f-15 may load data received from the primary RLCentity and data received from the secondary RLC entity onto differentcarriers and may transmit them, the primary RLC entity and the secondaryRLC entity having different logical channel identifiers. Theaforementioned procedure is about transmission of UL data, and when DLdata is received, the UE has to always receive the DL data to which thepacket duplication transmission is applied. That is, even when thepacket duplication transmission is inactivated with respect to a UL andthus the UE cannot duplicately transmit UL data to the secondary RLCentity, the secondary RLC entity 1 f-10 has to receive DL data from theMAC entity, to process the DL data, and thus to transmit the DL data tothe PDCP entity.

That is, when the packet duplication transmission is configured andactivated in the CA, the PDCP entity of the UE may duplicately transmitUL data to the primary RLC entity and the secondary RLC entity, and whenthe packet duplication transmission is configured and inactivated in theCA, the PDCP entity of the UE does not perform a duplication procedureon UL data and may transmit the UL data only to the primary RLC entity.Configuration of activation and inactivation of the packet duplicationtransmission may also be determined by a MAC control element.

When the packet duplication transmission configured through the RRCmessage is configured in Dual Connectivity (DC), the UE may configuretwo RLC entities, i.e., a primary RLC entity 1 f-16 and a secondary RLCentity 1 f-20, for a bearer or a PDCP entity to which the packetduplication transmission is configured. In a case where the packetduplication transmission is inactivated, when the PDCP entity transmitsa packet to a lower RLC entity in UL transmission, the PDCP entitytransmits the packet to a primary RLC entity and a secondary RLC entitybut does not duplicately process data as in operations of a split bearerand may transmit a plurality of pieces of different data to the primaryRLC entity and the secondary RLC entity, respectively. In a case wherethe packet duplication transmission is activated, in UL transmission,the PDCP entity may duplicately transmit a same packet to each of twolower RLC entities (the primary RLC entity and the secondary RLCentity). That is, the PDCP entity may transmit a packet to the primaryRLC entity, and may duplicate the packet and thus may transmit the samepacket to the secondary RLC entity.

When the packet duplication transmission is configured and activated inthe DC, MAC entities 1 f-25 and 1 f-30 may respectively load datareceived from the primary RLC entity and data received from thesecondary RLC entity onto different transport resources and may transmitthem to different BSs. The aforementioned procedure is abouttransmission of UL data, and when DL data is received, the UE has toalways receive the DL data to which the packet duplication transmissionis applied.

That is, when the packet duplication transmission is configured andactivated in the DA, the PDCP entity of the UE may duplicately transmitUL data to the primary RLC entity and the secondary RLC entity, and whenthe packet duplication transmission is configured and inactivated in theCA, the PDCP entity of the UE does not perform a duplication procedureon UL data and may transmit, as a split bearer, different data to theprimary RLC entity and the secondary RLC entity. Configuration ofactivation and inactivation of the packet duplication transmission mayalso be determined by a MAC control element.

Hereinafter, provided is a method of efficiently managing a case where amaximum retransmission count for preset data exceeds in two RLC entitiesconfigured with the packet duplication transmission.

When the maximum retransmission count for the preset data exceeds in anRLC entity that is connected to a primary cell (Pcell) from among thetwo RLC entities, the UE may trigger an RLF and may report occurrence ofthe RLF to the BS by using an RRC message. Then, the RLC entitydiscontinues transmission. All of a PDCP entity, an RLC entity, and aMAC entity may discontinue transmission, and may reconfigure RRCconnection.

However, when a maximum retransmission count for preset data exceeds inan RLC entity that is not connected to a primary cell (Pcell) but isconnected to a secondary cell (Scell) from among the two RLC entities,the UE may trigger a Scell RLF and may report, by using an RRC message,that the maximum retransmission count for preset data exceeds in the RLCentity connected to Scells. In order to indicate the RLC entitytriggered the Scell RLF, the RRC message may include a logical channelidentifier, a bearer identifier, and an indicator indicating a mastercell group (MCG) or a secondary cell group (SCG). For example, when avalue of a 1-bit indicator is 0, the indicator may indicate the MCG, andwhen the value is 1, the indicator may indicate the SCG. When the ScellRLF is triggered, the RLC entity, the PDCP entity, another RLC entity,and the MAC entity of the UE may continue transmitting data. Then, theUE may perform a necessary procedure, based on a response from the BSwith respect to the report on the Scell RLF.

For example, mapping between the RLC entity and a new cell (Pcell orScell) may be configured. The reason why the UE continues datatransmission even when the Scell RLF is triggered is because significanttransmission delay may occur if RRC connection is reconfigured due todeclaration of RLF, and because connection to Pcell is smooth, the UEmay solve the Scell RLF while the UE maintains data transmission.Furthermore, reception of DL data is not affected only when the RLCentity that triggered the Scell RLF still can transmit data. It isbecause DL data can be continuously transmitted only when an RLC statusreport on a DL is continuously transmitted.

According to some embodiments, the Pcell may refer to a cell configuredto have a physical uplink control channel (PUCCH) transport resource, toperform frequency measurement reporting, and to transmit or receive acontrol message with the BS, and the Scell may refer to a cell mainlyconfigured to transmit data. However, the disclosure is not limitedthereto.

Also, embodiments of the disclosure may be equally applied to a case inwhich a normal RLC entity that is not configured with the packetduplication transmission is not connected to the Pcell but is associatedwith or mapped to only Scells.

Hereinafter, provided is Embodiment 1 in which an RLC entity operatingin an AM calculates whether a maximum retransmission count for data tobe retransmitted exceeds, and when the maximum retransmission countexceeds, the excess is reported to its upper entity (e.g., an RRCentity).

The maximum retransmission count may be configured in at least one ofmessages of operations 1 e-10, 1 e-40, or 1 e-65 as described withreference to FIG. 1E, and may be indicated as a maxRetxThreshold value.

In Embodiment 1, a variable of RETX_COUNT may be defined and operatedfor each data (e.g., for each RLC SDU or RLC PDU) so as to record andstore a retransmission count for each data. Whenever retransmission foreach data is performed, the variable of RETX_COUNT may be managed bybeing increased by 1 and stored.

A detailed procedure proposed in Embodiment 1 will now be describedbelow.

When an RLC entity operating in an AM considers retransmission of data(e.g., an RLC SDU) or segmented data (e.g., a RLC SDU segment), the RLCentity performs a procedure below.

1. When the RLC entity first performs or considers retransmission of thedata (the RLC SDU) or the segmented data (the RLC SDU segment),

A. The RLC entity configures a RETX_COUNT value of the data to be 0.

2. Otherwise, that is, in a case where the RLC entity does not firstperform or consider retransmission of the data (the RLC SDU) or thesegmented data (the RLC SDU segment), when retransmission is not stoodby (reserved) with respect to the data (the RLC SDU) or the segmenteddata (the RLC SDU segment), and an increase due to another NACK of asame RLC status PDU did not occur in a RETX_COUNT value of the samedata,

A. The RETX_COUNT value is increased by 1.

3. When the RETX_COUNT value for the data is equal to a maximumretransmission count (maxRetxThreshold),

A. The RLC entity reports that a retransmission count has reached themaximum retransmission count to its upper entity (e.g., an RRC entity).

An example of the procedure is provided below.

Example 1

-   -   When an RLC SDU or an RLC SDU segment is considered for        retransmission, the transmitting side of the AM RLC entity        shall:    -   if the RLC SDU or RLC SDU segment is considered for        retransmission for the first time:    -   set the RETX_COUNT associated with the RLC SDU to zero.    -   else, if it (the RLC SDU or the RLC SDU segment that is        considered for retransmission) is not pending for retransmission        already and the RETX_COUNT associated with the RLC SDU has not        been incremented due to another negative acknowledgment in the        same STATUS PDU:    -   increment the RETX_COUNT.    -   if RETX_COUNT=maxRetxThreshold:    -   indicate to upper layers that max retransmission has been        reached

In the procedure above, when the RLC entity operating in the AM reports,to its upper entity (e.g., the RRC entity), that the maximumretransmission count has been reached, the upper entity may configureand transmit an RRC message to the BS so as to report an RLF when theRLC entity is connected to the Pcell. Then, each of entities (e.g., aPDCP entity, the RLC entity, or an MAC entity) may discontinue datatransmission. When the RLC entity is not connected to the Pcell but isconnected only to Scells, the upper entity may configure and transmit anRRC message to the BS so as to report a Scell RLF. Then, each of theentities (e.g., the PDCP entity, the RLC entity, or the MAC entity) maycontinue data transmission.

In the procedure above, when a retransmission count for preset datareaches a maximum retransmission count, the RLC entity is configured toreport to its upper entity, and when the RLC entity is connected to thePcell, the upper entity may trigger an RLF and may indicate each of theentities to discontinue transmission. However, when the RLC entity isnot connected to the Pcell but is connected only to the Scells, theupper entity may trigger a Scell RLF and may not perform particularindication on each of the entities, thereby allowing the entities tocontinue data transmission. Therefore, in a case where the Scell RLF istriggered, transmission and retransmission of data are continued in theRLC entity, and thus, a retransmission count for another data except forthe data for which the maximum retransmission count has been reached mayreach a maximum retransmission count. Accordingly, the RLC entity mayreport, to its upper entity (e.g., the RRC entity), that theretransmission count for the other data has reached the maximumretransmission count. Therefore, a Scell RLF may be reported a pluralityof times.

Thus, even when the upper entity (e.g., the RRC entity) receives aplurality of times an indication indicating that a retransmission counthas reached a maximum retransmission count from one RLC entity, theupper entity may perform a procedure of configuring an RRC message andreporting a Scell RLF to the BS only one time. After the RRC entityreports the Scell RLF, when a response thereto is not received from theBS in a preset time period, the RRC entity may re-transmit a Scell RLF.That is, in a case where a response to the Scell RLF is not receiveduntil a timer runs and then expires, when the timer expires, the RRCentity may re-perform reporting by re-transmitting the RRC message aboutthe Scell RLF to the BS.

Furthermore, according to some embodiments, the upper entity may defineand run a Scell-RLF reporting-prohibit timer, and, while the Scell-RLFreporting-prohibit timer is running, even when the upper entity receivesan indication indicating that a retransmission count has reached amaximum retransmission count from the RLC entity, the upper entity doesnot report a Scell RLF, and after a timer expires, the upper entity mayreport the Scell RLF, or when the indication indicating that aretransmission count has reached a maximum retransmission count isreceived after the Scell-RLF reporting-prohibit timer expires, the upperentity may report the Scell RLF.

Hereinafter, provided is Embodiment 2 in which the RLC entity operatingin an AM calculates whether a maximum retransmission count for data tobe retransmitted exceeds, and when the maximum retransmission countexceeds, the excess is reported to its upper entity (e.g., the RRCentity).

The maximum retransmission count may be configured in at least one ofmessages of operations 1 e-10, 1 e-40, or 1 e-65 as described withreference to FIG. 1E, and may be indicated as a maxRetxThreshold value.

In Embodiment 2, a variable of RETX_COUNT may be defined and operatedfor each data (e.g., for each RLC SDU or RLC PDU) so as to record andstore a retransmission count for each data. Whenever retransmission foreach data is performed, the variable of RETX_COUNT may be managed bybeing increased by 1 and stored.

A detailed procedure proposed in Embodiment 2 will now be describedbelow.

When the RLC entity operating in an AM considers retransmission of data(e.g., an RLC SDU) or segmented data (e.g., a RLC SDU segment), the RLCentity performs a procedure below.

1. When the RLC entity first performs or considers retransmission of thedata (the RLC SDU) or the segmented data (the RLC SDU segment),

A. the RLC entity configures a RETX_COUNT value of the data to be 0.

2. Otherwise, that is, in a case where the RLC entity does not firstperform or consider retransmission of the data (the RLC SDU) or thesegmented data (the RLC SDU segment), when retransmission is not stoodby with respect to the data (the RLC SDU) or the segmented data (the RLCSDU segment), and an increase due to another NACK of a same RLC statusPDU did not occur in a RETX_COUNT value of the same data,

A. the RETX_COUNT value is increased by 1.

3. When the RETX_COUNT value for the data is equal to a maximumretransmission count (maxRetxThreshold),

A. the RLC entity reports that a retransmission count has reached themaximum retransmission count to its upper entity (e.g., the RRC entity).

B. Then, the RLC entity does not consider retransmission of the data(the RLC SDU) or the segmented data (the RLC SDU segment).

An example of the procedure is provided below.

Example 1

When an RLC SDU or an RLC SDU segment is considered for retransmission,the transmitting side of the AM RLC entity shall:

-   -   if the RLC SDU or RLC SDU segment is considered for        retransmission for the first time:    -   set the RETX_COUNT associated with the RLC SDU to zero.    -   else, if it (the RLC SDU or the RLC SDU segment that is        considered for retransmission) is not pending for retransmission        already and the RETX_COUNT associated with the RLC SDU has not        been incremented due to another negative acknowledgment in the        same STATUS PDU:    -   increment the RETX_COUNT.    -   if RETX_COUNT=maxRetxThreshold:    -   indicate to upper layers that max retransmission has been        reached    -   do not consider any RLC SDU or RLC SDU segment for        retransmission.

In the procedure above, when the RLC entity operating in the AM reports,to its upper entity (e.g., the RRC entity), that the maximumretransmission count has been reached, the upper entity may configureand transmit an RRC message to the BS so as to report an RLF when theRLC entity is connected to the Pcell. Then, each of entities (e.g., aPDCP entity, the RLC entity, or an MAC entity) may discontinue datatransmission. When the RLC entity is not connected to the Pcell but isconnected only to Scells, the upper entity may configure and transmit anRRC message to the BS so as to report a Scell RLF. Then, each of theentities (e.g., the PDCP entity, the RLC entity, or the MAC entity) maycontinue data transmission.

In the procedure above, when a retransmission count for preset datareaches a maximum retransmission count, the RLC entity is configured toreport to its upper entity, and when the RLC entity is connected to thePcell, the upper entity may trigger an RLF and may indicate each of theentities to discontinue transmission. However, when the RLC entity isnot connected to the Pcell but is connected only to the Scells, theupper entity may trigger a Scell RLF and may not perform particularindication on each of the entities, thereby allowing the entities tocontinue data transmission.

In the procedure above, when a retransmission count for preset datareaches a maximum retransmission count, the RLC entity is configured toreport to its upper entity, but the upper entity does not considerretransmission of the data (the RLC SDU) or the segmented data (the RLCSDU segment), a retransmission count is not increased for any data.Therefore, a case in which an indication indicating that aretransmission count has reached a maximum retransmission count isreported to the upper entity a plurality of times does not occur.

Furthermore, after the upper entity (e.g., the RRC entity) or the RLCentity reports the Scell RLF, when a response thereto is not receivedfrom the BS in a preset time period, the RRC entity or the RLC entitymay re-transmit a Scell RLF or the indication indicating that aretransmission count has reached a maximum retransmission. That is, in acase where a response to the Scell RLF is not received until a timerruns and then expires, when the timer expires, the RRC entity mayre-perform reporting by re-transmitting the RRC message about the ScellRLF to the BS. Furthermore, according to some embodiments, the RLCentity may report again the indication indicating that a retransmissioncount has reached a maximum retransmission to the upper entity, and thusthe Scell RLF may be reported again to the BS.

Hereinafter, provided is Embodiment 3 in which the RLC entity operatingin an AM calculates whether a maximum retransmission count for data tobe retransmitted exceeds, and when the maximum retransmission countexceeds, the excess is reported to its upper entity (e.g., the RRCentity).

The maximum retransmission count may be configured in at least one ofmessages of operations 1 e-10, 1 e-40, or 1 e-65 as described withreference to FIG. 1E, and may be indicated as a maxRetxThreshold value.

In Embodiment 3, a variable of RETX_COUNT may be defined and operatedfor each data (e.g., for each RLC SDU or RLC PDU) so as to record andstore a retransmission count for each data. Whenever retransmission foreach data is performed, the variable of RETX_COUNT may be managed bybeing increased by 1 and stored.

A detailed procedure proposed in Embodiment 3 will now be describedbelow.

When the RLC entity operating in an AM considers retransmission of data(e.g., an RLC SDU) or segmented data (e.g., a RLC SDU segment), the RLCentity performs a procedure below.

1. When the RLC entity first performs or considers retransmission of thedata (the RLC SDU) or the segmented data (the RLC SDU segment),

A. the RLC entity configures a RETX_COUNT value of the data to be 0.

2. Otherwise, that is, in a case where the RLC entity does not firstperform or consider retransmission of the data (the RLC SDU) or thesegmented data (the RLC SDU segment), when retransmission is not stoodby with respect to the data (the RLC SDU) or the segmented data (the RLCSDU segment), and an increase due to another NACK of a same RLC statusPDU did not occur in a RETX_COUNT value of the same data,

A. the RETX_COUNT value is increased by 1.

3. When the RETX_COUNT value for the data is equal to a maximumretransmission count (maxRetxThreshold),

A. the RLC entity reports that a retransmission count has reached themaximum retransmission count to its upper entity (e.g., the RRC entity).

B. Then, the RLC entity does not consider retransmission of the data(the RLC SDU) or the segmented data (the RLC SDU segment) (thus, it ispossible to prevent the RETX_COUNT value for the data or the segmenteddata from increasing to a greater value).

An example of the procedure is provided below.

Example 1

When an RLC SDU or an RLC SDU segment is considered for retransmission,the transmitting side of the AM RLC entity shall:

-   -   if the RLC SDU or RLC SDU segment is considered for        retransmission for the first time:    -   set the RETX_COUNT associated with the RLC SDU to zero.    -   else, if it (the RLC SDU or the RLC SDU segment that is        considered for retransmission) is not pending for retransmission        already and the RETX_COUNT associated with the RLC SDU has not        been incremented due to another negative acknowledgment in the        same STATUS PDU:    -   increment the RETX_COUNT.    -   if RETX_COUNT=maxRetxThreshold:    -   indicate to upper layers that max retransmission has been        reached    -   do not consider the RLC SDU or RLC SDU segment for        retransmission.

In the procedure above, when the RLC entity operating in the AM reports,to its upper entity (e.g., the RRC entity), that the maximumretransmission count has been reached, the upper entity may configureand transmit an RRC message to the BS so as to report an RLF when theRLC entity is connected to the Pcell. Then, the upper entity maydiscontinue data retransmission with respect to each of entities. Whenthe RLC entity is not connected to the Pcell but is connected only toScells, the upper entity may configure and transmit an RRC message tothe BS so as to report a Scell RLF. Then, each of the entities (e.g.,the PDCP entity, the RLC entity, or the MAC entity) may continue datatransmission.

In the procedure above, when a retransmission count for preset datareaches a maximum retransmission count, the RLC entity is configured toreport to its upper entity, and when the RLC entity is connected to thePcell, the upper entity may trigger an RLF and may indicate each of theentities to discontinue transmission. However, when the RLC entity isnot connected to the Pcell but is connected only to the Scells, theupper entity may trigger a Scell RLF and may not perform particularindication on each of the entities, thereby allowing the entities tocontinue data transmission. Therefore, in a case where the Scell RLF istriggered, transmission and retransmission of data are continued in theRLC entity, and thus, a retransmission count for another data except forthe data for which the maximum retransmission count has been reached mayreach a maximum retransmission count. Accordingly, the RLC entity mayreport, to its upper entity (e.g., the RRC entity), that theretransmission count for the other data has reached the maximumretransmission count. Therefore, a Scell RLF may be reported a pluralityof times.

Thus, even when the upper entity (e.g., the RRC entity) receives aplurality of times an indication indicating that a retransmission counthas reached a maximum retransmission count from one RLC entity, theupper entity may perform a procedure of configuring an RRC message andreporting a Scell RLF to the BS only one time. After the RRC entityreports the Scell RLF, when a response thereto is not received from theBS in a preset time period, the RRC entity may re-transmit a Scell RLF.That is, in a case where a response to the Scell RLF is not receiveduntil a timer runs and then expires, when the timer expires, the RRCentity may re-perform reporting by re-transmitting the RRC message aboutthe Scell RLF to the BS.

Furthermore, according to some embodiments, the upper entity may defineand run a Scell-RLF reporting-prohibit timer, and, while the Scell-RLFreporting-prohibit timer is running, even when the upper entity receivesan indication indicating that a retransmission count has reached amaximum retransmission count from the RLC entity, the upper entity doesnot report a Scell RLF, and after a timer expires, the upper entity mayreport the Scell RLF, or when the indication indicating that aretransmission count has reached a maximum retransmission count isreceived after the Scell-RLF reporting-prohibit timer expires, the upperentity may report the Scell RLF.

Furthermore, according to some embodiments, the upper entity may defineand run a maximum retransmission count-reached indication prohibittimer, and, while the maximum retransmission count-reached indicationprohibit timer is running, even when a case where a retransmission counthas reached a maximum retransmission count occurs in the RLC entity, theRLC entity does not report the indication to the upper entity, and afterthe maximum retransmission count-reached indication prohibit timerexpires, the RLC entity may report the indication, or when aretransmission count has reached a maximum retransmission count afterthe maximum retransmission count-reached indication prohibit timerexpires, the RLC entity may report the indication.

Hereinafter, provided is Embodiment 4 in which the RLC entity operatingin an AM calculates whether a maximum retransmission count for data tobe retransmitted exceeds, and when the maximum retransmission countexceeds, the excess is reported to its upper entity (e.g., the RRCentity).

In the above descriptions, the maximum retransmission count may beconfigured in at least one of messages of operations 1 e-10, 1 e-40, or1 e-65 as described with reference to FIG. 1E, and may be indicated as amaxRetxThreshold value.

In Embodiment 4, a variable of RETX_COUNT may be defined and operatedfor each data (e.g., for each RLC SDU or RLC PDU) so as to record andstore a retransmission count for each data. Whenever retransmission foreach data is performed, the variable of RETX_COUNT may be managed bybeing increased by 1 and stored.

A detailed procedure proposed in Embodiment 4 will now be describedbelow.

When the RLC entity operating in an AM considers retransmission of data(e.g., an RLC SDU) or segmented data (e.g., a RLC SDU segment), the RLCentity performs a procedure below.

1. When the RLC entity first performs or considers retransmission of thedata (the RLC SDU) or the segmented data (the RLC SDU segment),

A. the RLC entity configures a RETX_COUNT value of the data to be 0.

2. Otherwise, that is, in a case where the RLC entity does not firstperform or consider retransmission of the data (the RLC SDU) or thesegmented data (the RLC SDU segment), when retransmission is not stoodby with respect to the data (the RLC SDU) or the segmented data (the RLCSDU segment), and an increase due to another NACK of a same RLC statusPDU did not occur in a RETX_COUNT value of the same data,

A. the RETX_COUNT value is increased by 1.

3. When the RETX_COUNT value for the data is equal to a maximumretransmission count (maxRetxThreshold),

A. in a case where the RLC entity (the RLC entity that retransmitted thedata) has not previously reported, to the upper entity, an indicationindicating that a retransmission count has reached a maximumretransmission count, the RLC entity reports the indication indicatingthat a retransmission count has reached a maximum retransmission countto the upper entity (e.g., the RRC entity).

B. Then, the RLC entity does not consider retransmission of the data(the RLC SDU) or the segmented data (the RLC SDU segment) (thus, it ispossible to prevent the RETX_COUNT value for the data or the segmenteddata from increasing to a greater value).

An example of the procedure is provided below.

Example 1

When an RLC SDU or an RLC SDU segment is considered for retransmission,the transmitting side of the AM RLC entity shall:

-   -   if the RLC SDU or RLC SDU segment is considered for        retransmission for the first time:    -   set the RETX_COUNT associated with the RLC SDU to zero.    -   else, if it (the RLC SDU or the RLC SDU segment that is        considered for retransmission) is not pending for retransmission        already and the RETX_COUNT associated with the RLC SDU has not        been incremented due to another negative acknowledgment in the        same STATUS PDU:    -   increment the RETX_COUNT.    -   if RETX_COUNT=maxRetxThreshold:    -   indicate to upper layers that max retransmission has been        reached if it has not been indicated before.    -   do not consider the RLC SDU or RLC SDU segment for        retransmission.

In the procedure above, when the RLC entity operating in the AM reports,to its upper entity (e.g., the RRC entity), that the maximumretransmission count has been reached, the upper entity may configureand transmit an RRC message to the BS so as to report an RLF when theRLC entity is connected to the Pcell. Then, each of entities (e.g., thePDCP entity, the RLC entity, or the MAC entity) may discontinue datatransmission. When the RLC entity is not connected to the Pcell but isconnected only to Scells, the upper entity may configure and transmit anRRC message to the BS so as to report a Scell RLF. Then, each of theentities (e.g., the PDCP entity, the RLC entity, or the MAC entity) maycontinue data transmission.

In the procedure above, when a retransmission count for preset datareaches a maximum retransmission count, the RLC entity is configured toreport to its upper entity, and when the RLC entity is connected to thePcell, the upper entity may trigger an RLF and may indicate each of theentities to discontinue transmission. However, when the RLC entity isnot connected to the Pcell but is connected only to the Scells, theupper entity may trigger a Scell RLF and may not perform particularindication on each of the entities, thereby allowing the entities tocontinue data transmission. Therefore, in a case where the Scell RLF istriggered, transmission and retransmission of data are continued in theRLC entity, and thus, a retransmission count for another data except forthe data for which the maximum retransmission count has been reached mayreach a maximum retransmission count. Accordingly, in a case where theretransmission count for the other data reaches the maximumretransmission count in the RLC entity, only when the RLC entity has notpreviously reported, to the upper entity, an indication indicating thata retransmission count has reached a maximum retransmission count, theRLC entity may report it to its upper entity (e.g., the RRC entity),such that it is possible to prevent reporting of unnecessaryindications.

According to some embodiments, after the upper entity (e.g., the RRCentity) reports the Scell RLF, when a response thereto is not receivedfrom the BS in a preset time period, the RRC entity may re-transmit aScell RLF. That is, in a case where a response to the Scell RLF is notreceived until a timer runs and then expires, when the timer expires,the upper entity may re-perform reporting by re-transmitting the RRCmessage about the Scell RLF to the BS.

Furthermore, according to some embodiments, the upper entity may defineand run a Scell-RLF reporting-prohibit timer, and, while the Scell-RLFreporting-prohibit timer is running, even when the upper entity receivesan indication indicating that a retransmission count has reached amaximum retransmission count from the RLC entity, the upper entity doesnot report a Scell RLF, and after a timer expires, the upper entity mayreport the Scell RLF, or when the indication indicating that aretransmission count has reached a maximum retransmission count isreceived after the Scell-RLF reporting-prohibit timer expires, the upperentity may report the Scell RLF.

Furthermore, according to some embodiments, the upper entity may defineand run a maximum retransmission count-reached indication prohibittimer, and, while the maximum retransmission count-reached indicationprohibit timer is running, even when a case where a retransmission counthas reached a maximum retransmission count occurs in the RLC entity, theRLC entity does not report the indication to the upper entity, and afterthe maximum retransmission count-reached indication prohibit timerexpires, the RLC entity may report the indication, or when aretransmission count has reached a maximum retransmission count afterthe maximum retransmission count-reached indication prohibit timerexpires, the RLC entity may report the indication.

FIG. 1G is a diagram for describing operations of a UE according to someembodiments of the disclosure.

The operations of the UE of FIG. 1G are based on Embodiment 4 from amongthe aforementioned embodiments. The UE of the disclosure may operateaccording to at least one of Embodiment 1 to Embodiment 4, and mayperform operations by combinations of some or all of the embodiments.

According to some embodiments, when a retransmission count for certaindata reaches a maximum retransmission count in an RLC entity of a UE 1g-01 which operates in an AM (operation 1 g-05), the UE checks whetheran indication indicating that the retransmission count of the RLC entityhas reached the maximum retransmission count is previously indicated toits upper entity (e.g., an RRC entity) (operation 1 g-10). That is, theUE may check whether a case where the retransmission count of the RLCentity has reached the maximum retransmission count is previouslyindicated or reported to the upper entity. When the case has beenpreviously indicated (or informed or reported), the UE does not indicatethat the retransmission count of the RLC entity has reached the maximumretransmission count (operation 1 g-15). When the case has not beenpreviously indicated, the UE indicates that the retransmission count ofthe RLC entity has reached the maximum retransmission count (operation 1g-20). Then, the UE does not perform anymore retransmission of data forwhich the retransmission count has reached the maximum retransmissioncount (operation 1 g-25). The UE may continuously perform newtransmission and retransmission of other data (operation 1 g-30).

As described above, when the packet duplication transmission is appliedin the next-generation mobile communication system, a method ofcalculating whether a maximum retransmission count for certain data hasbeen reached and an efficient method of reporting a Scell RLF in the RLCentity configured to transmit data to a Scell are provided, such that anincorrect operation of the UE may be prevented, and the UE may notunnecessarily report a Scell RLF to the BS a plurality of times.

FIG. 1H illustrates a configuration of a UE according to someembodiments of the disclosure.

Referring to FIG. 1H, the UE includes a Radio Frequency (RF) processor 1h-10, a baseband processor 1 h-20, a storage 1 h-30, and a controller 1h-40. However, the UE is not limited thereto and may include moreelements than the elements shown in FIG. 1H or may include less elementsthan the shown elements.

The RF processor 1 h-10 may perform functions for transmitting andreceiving signals through radio channels, e.g., band conversion andamplification of the signals. That is, the RF processor 1 h-10 mayup-convert a baseband signal provided from the baseband processor 1h-20, into an RF band signal and then may transmit the RF band signalthrough an antenna, and may down-convert an RF band signal receivedthrough the antenna, into a baseband signal. For example, the RFprocessor 1 h-10 may include a transmit filter, a receive filter, anamplifier, a mixer, an oscillator, a digital-to-analog convertor (DAC),an analog-to-digital convertor (ADC), or the like. Although only oneantenna is illustrated in FIG. 1H, the UE may include a plurality ofantennas. The RF processor 1 h-10 may include a plurality of RF chains.The RF processor 1 h-10 may perform beamforming. For beamforming, the RFprocessor 1 h-10 may adjust phases and intensities of signals to betransmitted or received through a plurality of antennas or antennaelements. The RF processor 1 h-10 may perform a MIMO operation and mayreceive a plurality of layers in the MIMO operation. In response to thecontrol by the controller 1 h-40, the RF processor 1 h-10 may performreceived beam sweeping by appropriately configuring a plurality ofantennas or antenna elements, or may adjust a direction and a beam widthof a received beam to coordinate with a transmit beam.

The baseband processor 1 h-20 may convert between a baseband signal anda bitstream based on physical entity specifications of a system. Forexample, for data transmission, the baseband processor 1 h-20 maygenerate complex symbols by encoding and modulating a transmitbitstream. For data reception, the baseband processor 1 h-20 mayreconstruct a received bitstream by demodulating and decoding a basebandsignal provided from the RF processor 1 h-10. For example, according toan OFDM scheme, for data transmission, the baseband processor 1 h-20 maygenerate complex symbols by encoding and modulating a transmitbitstream, may map the complex symbols to subcarriers, and then mayconfigure OFDM symbols by performing inverse fast Fourier transform(IFFT) and cyclic prefix (CP) insertion. For data reception, thebaseband processor 1 h-20 may segment a baseband signal provided fromthe RF processor 1 h-10, into OFDM symbol units, may reconstruct signalsmapped to subcarriers by performing fast Fourier transform (FFT), andthen may reconstruct a received bitstream by demodulating and decodingthe signals.

The baseband processor 1 h-20 and the RF processor 1 h-10 may transmitand receive signals as described above. The baseband processor 1 h-20and the RF processor 1 h-10 may also be called a transmitter, areceiver, a transceiver, or a communicator. At least one of the basebandprocessor 1 h-20 and the RF processor 1 h-10 may include a plurality ofcommunication modules to support a plurality of different radio accesstechnologies. At least one of the baseband processor 1 h-20 and the RFprocessor 1 h-10 may include different communication modules to processsignals of different frequency bands. For example, the different radioaccess technologies may include an LTE network, an NR network, or thelike. The different frequency bands may include a super-high frequency(SHF) (e.g., 2.2 GHz, 2 GHz) band and a millimeter wave (mmWave) (e.g.,60 GHz) band. The UE may transmit and receive signals to and from the BSby using the baseband processor 1 h-20 and the RF processor 1 h-10. Inthis regard, the signals may include control information and data.

The storage 1 h-30 may store basic programs, application programs, anddata, e.g., configuration information, for operations of the UE. Thestorage 1 h-30 may provide the stored data upon request by thecontroller 1 h-40. The storage 1 h-30 may include any or a combinationof storage media such as read-only memory (ROM), random access memory(RAM), a hard disk, a compact disc (CD)-ROM, and a digital versatiledisc (DVD). The storage 1 h-30 may include a plurality of memories.According to some embodiments, the storage 1 h-30 may store a programfor performing the wireless communication method for reporting a ScellRLF.

The controller 1 h-40 may control overall operations of the UE. Forexample, the controller 1 h-40 transmits and receives signals throughthe baseband processor 1 h-20 and the RF processor 1 h-10. Furthermore,the controller 1 h-40 records and reads data on or from the storage 1h-30. To this end, the controller 1 h-40 may include at least oneprocessor. For example, the controller 1 h-40 may include acommunication processor (CP) for controlling communications and anapplication processor (AP) for controlling an upper layer such as anapplication program. Furthermore, at least one element in the UE may beimplemented as a chip. FIG. 1I is a block diagram of atransmission/reception point (TRP) in a wireless communication system,according to some embodiments of the disclosure.

Referring to FIG. 1I, the BS may include a RF processor 1 i-10, abaseband processor 1 i-20, a communicator 1 i-30, a storage 1 i-40, anda controller 1 i-50. However, the TRP is not limited thereto and mayinclude more elements than the elements shown in FIG. 1I or may includeless elements than the shown elements.

The RF processor 1 i-10 may perform functions for transmitting andreceiving signals through radio channels, e.g., band conversion andamplification of the signals. That is, the RF processor 1 i-10 mayup-convert a baseband signal provided from the baseband processor 1i-20, into an RF band signal and then may transmit the RF band signalthrough an antenna, and may down-convert an RF band signal receivedthrough an antenna, into a baseband signal. For example, the RFprocessor 1 i-10 may include a transmit filter, a receive filter, anamplifier, a mixer, an oscillator, a DAC, an ADC, or the like. Althoughonly one antenna is illustrated in FIG. 1I, the RF processor 1 i-10 mayinclude a plurality of antennas. Also, the RF processor 1 i-10 mayinclude a plurality of RF chains. In addition, the RF processor 1 i-10may perform beamforming. For beamforming, the RF processor 1 i-10 mayadjust phases and intensities of signals to be transmitted or receivedthrough a plurality of antennas or antenna elements. The RF processor 1i-10 may perform a DL MIMO operation by transmitting one or more layers.

The baseband processor 1 i-20 may convert between a baseband signal anda bitstream based on physical entity specifications of a radio accesstechnology. For example, for data transmission, the baseband processor 1i-20 generates complex symbols by encoding and modulating a transmitbitstream. For data reception, the baseband processor 1 i-20 mayreconstruct a received bitstream by demodulating and decoding a basebandsignal provided from the RF processor 1 i-10. For example, according toan OFDM scheme, for data transmission, the baseband processor 1 i-20generates complex symbols by encoding and modulating a transmitbitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols by performing IFFT and CP insertion. For data reception,the baseband processor 1 i-20 may segment a baseband signal providedfrom the RF processor 1 i-10, into OFDM symbol units, may reconstructsignals mapped to subcarriers by performing FFT, and then mayreconstruct a received bitstream by demodulating and decoding thesignals. The baseband processor 1 i-20 and the RF processor 1 i-10 maytransmit and receive signals as described above. As such, the basebandprocessor 1 i-20 and the RF processor 1 i-10 may also be called atransmitter, a receiver, a transceiver, a communicator, or a wirelesscommunicator. The BS may transmit and receive signals to and from the UEby using the baseband processor 1 i-20 and the RF processor 1 i-10. Inthis regard, the signals may include control information and data.

The communicator 1 i-30 may provide an interface for communicating withother nodes in a network. According to some embodiments, thecommunicator 1 i-30 may be a backhaul communicator.

The storage 1 i-40 may store basic programs, application programs, anddata, e.g., configuration information, for operations of the BS. Thestorage 1 i-40 may store, for example, information about bearersassigned for a connected UE and measurement results reported from theconnected UE. The storage 1 i-40 may store criteria information used todetermine whether to provide or release dual connectivity to or from theUE. The storage 1 i-40 may provide the stored data upon request by thecontroller 1 i-50. The storage 1 i-40 may include any or a combinationof storage media such as ROM, RAM, a hard disk, a CD-ROM, and a DVD. Thestorage 1 i-40 may include a plurality of memories. According to someembodiments, the storage 1 i-40 may store a program for performing thewireless communication method for reporting a Scell RLF.

The controller 1 i-50 may control overall operations of the BS. Forexample, the controller 1 i-50 transmits and receives signals throughthe baseband processor 1 i-20 and the RF processor 1 i-10, or thecommunicator 1 i-30. The controller 1 i-50 records and reads data on orfrom the storage 1 i-40. To this end, the controller 1 i-50 may includeat least one processor. Furthermore, at least one element in the TRP maybe implemented as a chip.

FIG. 2A is a diagram illustrating a configuration of an LTE system,according to some embodiments of the disclosure.

According to some embodiments, an NR system may have a configurationcorresponding to that of FIG. 2A. Referring to FIG. 2A, a wirelesscommunication system includes a plurality of eNBs 2 a-05, 2 a-10, 2a-15, and 2 a-20, an MME 2 a-25, and an S-GW 2 a-30. A UE 2 a-35 mayaccess an external network via the eNBs 2 a-05, 2 a-10, 2 a-15, or 2a-20 and the S-GW 2 a-30.

The eNBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20 refer to access nodes of acellular network and provide a wireless access to UEs that access thenetwork. That is, in order to service traffic of users, the eNBs 2 a-05,2 a-10, 2 a-15, and 2 a-20 perform scheduling by collating statusinformation, e.g., buffer status information, available transmissionpower status information, and channel state information of UEs, and thussupport connection between the UEs and a core network (CN). The MME 2a-25 is an entity for performing a mobility management function andvarious control functions on a UE and may be connected to the pluralityof eNBs. The S-GW 2 a-30 may be an entity for providing data bearers.Furthermore, the MME 2 a-25 and the S-GW 2 a-30 may further performauthentication, bearer management, or the like with respect to a UEattempting to access the network, and may process packets received fromthe eNBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20 or packets to be transferredto the eNBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20.

FIG. 2B illustrates radio protocol architectures of an LTE system and anNR system to be referenced for descriptions of the disclosure.

Referring to FIG. 2B, radio protocols of the LTE system may include PDCPentities 2 b-05 and 2 b-40, RLC entities 2 b-10 and 2 b-35, and MACentities 2 b-15 and 2 b-30 respectively in a UE and eNB/gNB. Obviously,the disclosure is not limited to the above example.

With respect to an MAC entity, a UE includes MAC entities correspondingto the number of BSs that are simultaneously configured. For example,when the UE communicates with one BS, one MAC entity is present, andwhen the UE uses a DC technique of simultaneously communicating with twoBSs, two MAC entities for the respective BSs are present in the UE.

According to some embodiments, the PDCP entity 2 b-05 or 2 b-40 performsoperations of IP header compression/decompression, and the RLC entity 2b-10 or 2 b-35 reconfigures PDCP PDUs to appropriate sizes. The MACentity 2 b-15 or 2 b-30 may be connected to a plurality of RLC entitiesconfigured for one UE and may multiplex RLC PDUs into a MAC PDU and maydemultiplex the RLC PDUs from the MAC PDU.

A physical (PHY) entity 2 b-20 or 2 b-25 may channel-code and modulateupper layer data into OFDM symbols and transmit the OFDM symbols througha radio channel, or may demodulate OFDM symbols received through a radiochannel and channel-decode and deliver the OFDM symbols to an upperlayer. In order to additionally correct an error, the PHY entity may useHARQ, and a receiver may transmit, by using 1 bit, whether or not apacket transmitted from a transmitter is received. This is called HARQACK/NACK information. In the LTE system, DL HARQ ACK/NACK informationabout UL data transmission is transmitted through a Physical Hybrid-ARQIndicator Channel (PHICH) physical channel, and in the NR system, a UEmay determine, based on scheduling information for the UE, whetherretransmission or new transmission through a Physical Dedicated ControlChannel (PDCCH) that is a channel through which DL/UL resourceallocation is transmitted is requested. This is because asynchronousHARQ is applied in the NR system.

According to some embodiments, UL HARQ ACK/NACK information about DLdata transmission may be transmitted through a PUCCH or Physical UplinkShared Channel (PUSCH) physical channel. The PUCCH is transmitted in aUL of a PCell to be described below, but, when a UE supports, a BS mayallow a SCell to additionally transmit it to the UE, and this is calledthe PUCCH SCell.

Although not illustrated in drawings, RRC entities are present above thePDCP entities of the UE and the BS, respectively, and each of the RRCentities may transmit or receive configuration control messages relatedto access and measurement to control radio resources.

The PHY entity may be configured to correspond to one or morefrequencies/carriers, and a technology by which a plurality offrequencies are simultaneously configured and used is referred to as theCA technology. Only one carrier was used to be used for communicationbetween a UE and an E-UTRAN NodeB (eNB), but, according to the CAtechnology, one main carrier and one or more subcarriers areadditionally used such that an amount of data transmission may besignificantly increased as much as the number of subcarriers. In the LTEsystem, a cell in a BS which uses a main carrier is referred to as amain cell or PCell, and a cell in the BS which uses a subcarrier isreferred to as a sub-cell or a SCell.

FIG. 2C illustrates DL and UL channel frame structures when a beam-basedcommunication is performed in an NR system, according to someembodiments of the disclosure.

In FIG. 2C, a BS 2 c-01 may transmit signals in the form of beams 2c-11, 2 c-13, 2 c-15, and 2 c-17 so as to transmit the signals via widercoverage or to transmit strong signals. A UE 2 c-03 within a cell needsto transmit or receive data by using a particular beam (beam #1 2 c-13in FIG. 2C) transmitted by the BS.

According to some embodiments, whether or not a UE is connected to a BS,states of the UE are classified into an idle mode (RRC IDLE) and aconnected mode (RRC CONNECTED). Thus, the BS may not detect a locationof the UE in the idle mode.

When the UE in the idle mode attempts to switch its state to a connectedmode state, the UE receives Synchronization Signal Blocks (SSBs) 2 c-21,2 c-23, 2 c-25, and 2 c-27 transmitted from the BS. An SSB is an SSBsignal that is periodically transmitted at intervals configured by theBS, and each SSB is segmented to a Primary Synchronization Signal (PSS)2 c-41, a Secondary Synchronization Signal (SSS) 2 c-43, and a PhysicalBroadcast Channel (PBCH) (2 c-45).

In FIG. 2C, a scenario in which SSBs are transmitted by using respectivebeams is assumed. For example, it is assumed that SSB #0 2 c-21 istransmitted by using beam #0 2 c-11, SSB #1 2 c-23 is transmitted byusing beam #1 2 c-13, SSB #2 2 c-25 is transmitted by using beam #2 2c-15, and SSB #3 2 c-27 is transmitted by using beam #3 2 c-17. Withreference to FIG. 2C, it is assumed that an idle-mode UE is located onbeam #1, but even when a connected-mode UE performs a random access, theUE selects an SSB that is received when the random access is performed.

Referring to FIG. 2C, the UE 2 c-03 receives SSB #1 2 c-23 transmittedusing beam #1 2 c-13. Upon reception of SSB #1 2 c-23, the UE may obtaina Physical Cell Identifier (PCI) of the BS by referring to a PSS and aSSS, and may receive a PBCH, thereby identify that an identifier (i.e.,#1) of the currently received SSB, in which location within a 10 msframe the current SSB is received, and in which System Frame Number(SFN) the SSB is present in SFNs having an interval of 10.24 seconds.Furthermore, the PBCH includes a Master Information Block (MIB), and theMIB includes information indicating at which location a systeminformation block type 1 (SIB1) that broadcasts detailed configurationof a cell may be received. Upon reception of SIB1, the UE may detect atotal number of SSBs transmitted by the BS, and may detect a location ofa Physical Random Access Channel (PRACH) occasion in which the UE canperform a random access to switch to a connected mode state (moreparticularly, the UE can transmit a preamble that is specially designedto synchronize UL synchronization) (in FIG. 2C, a scenario where PRACHoccasion is allocated at every 1 ms is assumed, and referring to FIG.2C, the UE can detect PRACH occasions 2 c-30 to 2 c-39).

Furthermore, the UE may detect, based on SIB1 information, which PRACHoccasion from among the PRACH occasions 2 c-30 to 2 c-39 is to be mappedto which SSB index. For example, in FIG. 2C, the scenario where PRACHoccasion is allocated at every 1 ms is assumed, and in the scenario, ½SSB is allocated to one PRACH occasion (i.e., two PRACH occasions perone SSB). Accordingly, FIG. 2C illustrates the scenario in which twoPRACH occasions are allocated to each SSB, the two PRACH occasionsstarting from a PRACH occasion based on an SFN value. That is, PRACHoccasions 2 c-30 and 2 c-31 may be allocated for SSB #0, and PRACHoccasions 2 c-32 and 2 c-33 may be allocated for SSB #1. When a PRACHoccasion is allocated to all SSBs, PRACH occasions 2 c-38 and 2 c-39 maybe allocated again to an initial SSB.

The UE recognizes locations of PRACH occasions 2 c-32 and 2 c-33 for SSB#1, and transmits a random access preamble in an earlier PRACH occasion(e.g., 2 c-32) from among PRACH occasions 2 c-32 and 2 c-33corresponding to SSB #1. Because the BS receives the preamble in PRACHoccasion 2 c-32, the BS may recognize that the UE has transmitted thepreamble by selecting SSB #1, and when a random access is performed,data may be transmitted or received on a beam corresponding to SSB #1.

When a UE in a connected state moves to a target BS from a current(source) BS due to handover, etc., the UE performs a random access onthe target BS, and performs an operation of transmitting the randomaccess preamble by selecting an SSB as described above. Furthermore, inthe handover, the source BS transmits a handover command to the UE toswitch from the source BS to the target B S, and a handover commandmessage transmitted from the source BS may include a UE-dedicated randomaccess preamble identifier for each SSB of the target BS, which isallocated by the target BS, for the UE can use when the UE performs arandom access on the target BS.

According to some embodiments, a BS may not allocate dedicated randomaccess preamble identifiers to all beams, in consideration of a currentlocation of a UE. Therefore, dedicated random access preambles may notbe allocated to some SSBs (e.g., dedicated random access preambles areallocated only to Beams #2 and #3). In a case where a dedicated randomaccess preamble is not allocated to an SSB the UE selects fortransmission of a preamble, the UE randomly selects a contention-basedrandom access preamble and then performs a random access. For example,in FIG. 2C, after the UE first located on Beam #1 and then performed arandom access but failed, when the UE re-transmits a random accesspreamble, the UE may locate on Beam #3 and may transmit a dedicatedpreamble. That is, when retransmission of a preamble occurs during onerandom access procedure, whether a dedicated random access preamble isallocated to a selected SSB at every transmission of a preamble, acontention-based random access procedure and a contention-free randomaccess procedure may coexist.

FIG. 2D illustrates contention-based and contention-free random accessprocedures performed in a situation such as handover by a UE to a BS,according to some embodiments of the disclosure.

A random access procedure may include a contention-based random accessprocedure and a contention-free random access procedure, and in thecontention-free random access procedure, a procedure in which the BSallocates a dedicated random access resource to the UE so as to allowthe UE to perform a contention-free random access exists before a randomaccess. The dedicated random access resource may refer to a particularpreamble index and/or a PRACH resource on a particular time/frequency.Also, information for allocating the dedicated random access resourcemay be allocated through a PDCCH or may be transmitted through an RRClayer message. The RRC layer message may include an RRCReconfigurationmessage (e.g., for handover). Therefore, in a case where a dedicatedrandom access resource allocated by the BS is present for SSB/ChannelState Information Reference Signal (CSI-RS) the UE selects for a randomaccess procedure that is being currently performed, the UE transmits arandom access preamble on the corresponding random access resource.Also, in a contention-free random access, when a preamble transmitted bythe UE is present in a Random Access Response (RAR) message to bedescribed below, the UE determines that the random access issuccessfully completed, and thus ends a random access procedure.

FIG. 2D illustrates an assumed case in which, when a handover command isreceived from a previous source BS in a handover situation, a preambleidentifier M is received for SSB #3.

Accordingly, a UE 2 d-01 first moves to a target BS 2 d-03 (alsoreferred to as the gNB 2 d-03), and then determines on which beam the UE2 d-01 is requested to perform data transmission and reception includinga random access, and selects a SSB, based on the determination(operation 2 d-63). According to a method of selecting an SSB, a BStransmits a preset threshold through a SIB1 or configuration informationin a handover message, and a UE selects one of received SSBs whosesignal power exceeds the threshold. For example, in FIG. 2C, in a casewhere the UE receives all of SSB #0, SSB #1, and SSB #2, but only asignal power of SSB #1 exceeds the threshold and signal powers of SSB #0and SSB #2 do not exceed the threshold, the UE may select SSB #1. Thethreshold may be configured through the SIB1 or a message of an RRCentity which is directly provided to the UE, and may be indicated asrsrp-ThresholdSSB or rsrp-ThresholdCSl-RS which is a value of aReference Signal Received Power (RSRP) of a SSB or a RSRP of a CSI-RS.

As described above, when the UE selects the SSB, the UE may detect aPRACH Occasion mapped to the selected SSB and then may transmit, to theBS, a random access preamble in the PRACH Occasion (operation 2 d-11).In this regard, because a dedicated preamble is not allocated to SSB #1,a contention-based random access may be performed. That is, one ofcontention-based preamble identifiers may be randomly selected and thentransmitted (in drawing, it is assumed that #N is selected andtransmitted).

Also, a case in which one or more UEs simultaneously transmit randomaccess preambles in a PRACH Occasion may occur. That is, another UE mayrandomly select a resource and may perform transmission using theresource, and may equally select preamble #N. A PRACH resource mayextend over one subframe or only some symbols in one subframe may beused. PRACH resource information may be included in system informationor configuration information in a handover command, which is broadcastby the BS, such that the UE may know, based on the PRACH resourceinformation, in which time and frequency resources a preamble has to betransmitted. Also, a plurality of preamble identifiers (indices) may bepresent for random access preambles according to a standard as aparticular sequence uniquely designed to be receivable when the randomaccess preambles are transmitted before synchronization with the BS iscompleted. When the plurality of preamble identifiers (indices) arepresent, a preamble to be transmitted by the UE may be randomly selectedby the UE or may be specified by the BS.

Also, in a case where the UE in a connected mode state in a procedure ofselecting an SSB performs a random access, when the BS previouslyconfigures a particular signal to be measured, the UE may select a PRACHoccasion, based on the particular signal to be measured, instead of theSSB. The particular signal to be measured may be a SSB or a CSI-RS. Forexample, when the UE performs handover to a different BS due to movementof the UE, the UE may select a PRACH occasion mapped to a SSB or aCSI-RS of a target BS which is included in a handover command. The UEmeasures a configured signal, thereby determining in which PRACHoccasion a random access preamble is to be transmitted.

When the BS receives the preamble transmitted by the UE 2 d-01 (or apreamble transmitted by another UE), the BS may transmit an RAR messagewith respect to the received preamble to the UE (operation 2 d-21). TheRAR message may include preamble identifier information used inoperation 2 d-11, UL transmission timing advance adjust information, ULresource allocation information to be used in operation thereafter,temporary UE identifier information, and the like.

According to some embodiments, when a plurality of UEs attempt randomaccesses by transmitting different preambles in operation 2 d-11, thepreamble identifier information may be included to indicate for whichpreamble the RAR message transmitted by the BS is a response message.

According to some embodiments, the UL resource allocation informationrefers to detailed information of a resource to be used by the UE, andmay include a modulation and coding scheme (MCS) to be used intransmission, power adjustment information for transmission, or thelike.

According to some embodiments, when the UE that transmits a preambleperforms an initial access, the UE does not have an identifier allocatedby the BS for communication with the BS, and thus the temporary UEidentifier information is transmitted as a value to be used as theidentifier.

The RAR message has to be transmitted within a preset time period aftera preset time elapses after the UE transmits the preamble, and thepreset time period is referred to as an “RAR window” (operations 2 d-51and 2 d-53). The RAR window starts after the preset time elapses after avery first preamble is transmitted. According to some embodiments, thepreset time may have a value of a subframe unit (2 ms) or a smallervalue. However, the disclosure is not limited to the above example.Furthermore, a length of the RAR window may be configured in a systeminformation message or a handover command message which is broadcast bythe BS.

When the RAR window is transmitted, the BS schedules a corresponding RARmessage through a PDCCH, and its scheduling information is scrambled bya Random Access-Radio Network Temporary Identifier (RA-RNTI). TheRA-RNTI is mapped to a PRACH resource used in transmission of the randomaccess preamble message (in operation 2 d-11), and the UE that transmitsthe preamble in the particular PRACH resource attempts reception of aPDCCH based on the RA-RNTI, thereby determining whether there is acorresponding RAR message. When the RAR message is a response to thepreamble the UE transmitted in operation 2 d-11 as in FIG. 2D, theRA-RNTI used in scheduling information about the RAR message may includeinformation about transmission in operation 2 d-11. To do so, theRA-RNTI may be calculated according to Equation below.RA-RNTI=1+s_id+14×t_id+14×80×f_id+14×80×8×ul_carrier_id

In this regard, s_id refers to an index corresponding to a first OFDMsymbol in which transmission of the preamble transmitted in operation 2d-11 is started, and has a value of 0≤s_id<14 (that is, a maximum numberof OFDM symbols in one slot). Also, t_id refers to an indexcorresponding to a first slot in which transmission of the preambletransmitted in operation 2 d-11 is started, and has a value of 0≤t_id<80(that is, a maximum number of slots in one system frame (20 ms)). Also,f_id indicates which ordinal number of PRACH resource the preambletransmitted in operation 2 d-11 is transmitted on frequency, and has avalue of 0≤f_id<8 (that is, a maximum number of PRACHs on frequency in asame time). ul carrier id may be a parameter that, when using twocarriers as UL with respect to a single cell, distinguishes whether thepreamble is transmitted in a normal UL (NUL) (0 in this case) or whetherthe preamble is transmitted in a supplementary UL (SUL) (1 in thiscase).

With reference to FIG. 2D, the scenario is assumed, in which the UEreceives the RAR message based on the RA-RNTI corresponding to thetransmission in operation 2 d-11, and the corresponding message includesa response to preamble #N transmitted by the UE. Therefore, the UE fillsa message to be transmitted in an Msg3 buffer (in a contention-basedrandom access, a preamble is called Msg1, a RAR is called Msg2, amessage to be transmitted thereafter in a UL is called Msg3, and amessage to be received thereafter in a DL is called Msg4, and data to betransmitted in the Msg3 is called the Msg3 buffer) in the UE accordingto a UL resource size for Msg3 allocated in the RAR message (operation 2d-71).

The scenario in FIG. 2D is assumed for a scenario in which the UE in aconnected mode performs handover, and thus, the UE is already allocatedan identifier within cell (C-RNTI) to be used within a target BS,through the handover command message. The UE may include, in the Msg3,C-RNTI MAC Control Element ((C-RNTI MAC CE) that is a control message ofa MAC entity) for indicating that the UE that currently attempts arandom access is the UE of the C-RNTI generates data with a handovercompletion message, based on the UL resource size allocated in the RARmessage, and transmits the Msg3 (operation 2 d-13).

However, with reference to FIG. 2D, the scenario is assumed, in whichtransmission of the Msg3 fails (operation 2 d-13). That is, the UEtransmits the Msg3, and starts a ra-ContentionResolutionTimer timer.When a response to the transmitted Msg3 is not received until thera-ContentionResolutionTimer timer expires (operation 2 d-73), the UEdetermines that the Msg3 has not been correctly transmitted, and startsa procedure of re-transmitting a random access preamble.

That is, when the ra-ContentionResolutionTimer timer expires, the UEselects again an SSB at a corresponding time point so as to retransmit apreamble (operation 2 d-63). Here, it is assumed that the selected SSBis Beam #3 in FIG. 2C. That is, as described above, a case is assumed,in which the UE receives a preamble identifier M for SSB #3 when the UEreceives a handover command. Accordingly, the BS retransmits a dedicatedpreamble in a PRACH occasion corresponding to SSB #3 (operation 2 d-15),waits for a response thereto (operation 2 d-53) and re-receives an RARmessage (operation 2 d-23). Because the UE has performed acontention-free random access by performing a random access by using thededicated preamble, the UE assumes that the random access issuccessfully completed only when the RAR is received.

Because the re-received RAR message (operation 2 d-23) includes ULresource allocation information, the UE may transmit a UL on theresource even when the random access has been already succeeded(operation 2 d-75).

In order to transmit the Msg3 so as to perform the previouscontention-based random access, the UE already filled the data in theMsg3 buffer. In a case where the data is present in the Msg3 buffer, theUE has to changelessly transmit it to a physical entity. For example, ina case where the size of the UL resource allocation received in the RAR(operation 2 d-21) received in the contention-based random access is 56bytes, and the data in the Msg3 buffer is generated according to 56bytes, when the contention-based random access fails and then thecontention-free random access is performed according to SSB/CSI-RSselected thereafter, the BS may allocate a very large size (e.g., 200bytes) to the UE. In this case, the UE cannot changelessly transmit aPDU that is already generated in the Msg3 buffer and thus may need tosolve this issue.

FIG. 2E is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 1 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2E, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 e-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 e-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 e-09).

Afterward, when the UE succeeds in the contention-free random access andthus receives an RAR message in response to the preamble, the UEdetermines the following so as to transmit data on a UL resourceassigned in the RAR message:

In a case where the RAR message is not a first RAR successfully receivedin a random access procedure, and the UE determines that a size of a MACPDU stored in an Msg3 buffer is different from a size of UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 e-11), the UE re-generates (or re-builds) the MACPDU according to the size of the UL resource allocation received in theRAR message and re-stores the MAC PDU in the Msg3 buffer (operation 2e-13). The UE may re-generate the MAC PDU by excluding some MAC subPDUsand including some MAC subPDUs from among MAC subPDUs (sub units thatconstitute the MAC PDU) that were to be transmitted and are stored inthe Msg3 buffer. For example, the UE may re-generate the MAC PDU byincluding a handover completion RRC message. Also, the UE may add, tothe re-generated MAC PDU, a Buffer Status Report (BSR) MAC CE forreporting a buffer status so as to transmit UL data, but it is notnecessary to include a MAC CE such as the aforementioned C-RNTI MAC CEin the Msg3 that occurs after the contention-free random access (becausethe BS already knows which UE has transmitted the preamble), and thusthe MAC CE such as the aforementioned C-RNTI MAC CE may be excluded.Also, depending on necessity, the UE may include or may not include aPower Headroom Report (PHR) MAC CE for indicating remaining power for ULby the UE in the re-generated MAC PDU.

Afterward, the UE determines whether a packet is stored in the Msg3buffer, and when the packet is stored, the UE transmits the packet inthe Msg3 buffer on the UL resource received in the RAR message(operation 2 e-15).

FIG. 2F is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 2 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2F, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 f-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 f-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 f-09).

Afterward, the UE succeeds in the contention-free random access anddetermines whether the UE receives an RAR message in response to thepreamble (operation 2 f-11).

When it is successful, as there is data in an Msg3 buffer which isstored during a previous contention-free random access, the UE obtains apacket from the Msg3 buffer so as to transmit it (operation 2 f-13).When the UE determines that a size of the obtained packet is differentfrom a size of UL resource allocation received in the RAR message (or,when the UE determines that the size of the UL resource allocationreceived in the RAR message is greater) (operation 2 f-15), the UEre-generates the MAC PDU according to the size of the UL resourceallocation received in the RAR message (operation 2 f-17).Alternatively, when transmission of the preamble is not selected fromamong contention-based random access preambles (i.e., selection of adedicated random access preamble) and the UE determines that the size ofthe obtained packet is different from the size of the UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 f-15), the UE re-generates the MAC PDU accordingto the size of the UL resource allocation received in the RAR message(operation 2 f-17). The UE may re-generate the MAC PDU by excluding someMAC subPDUs and including some MAC subPDUs from among MAC subPDUs thatwere to be transmitted from the Msg3 buffer. For example, the UE mayre-generate the MAC PDU by including a handover completion RRC message.Also, the UE may add, to the re-generated MAC PDU, a BSR MAC CE forreporting a buffer status so as to transmit UL data, but it is notnecessary to include a MAC CE such as the aforementioned C-RNTI MAC CEin the Msg3 that occurs after the contention-free random access (becausethe BS already knows which UE has transmitted the preamble), and thusthe MAC CE such as the aforementioned C-RNTI MAC CE may be excluded.Also, depending on necessity, the UE may include or may not include aPHR MAC CE for indicating remaining power for UL by the UE in there-generated MAC PDU.

Afterward, the UE transmits the packet (the MAC PDU) on the UL resourcereceived in the RAR message, the packet being re-generated according tothe aforementioned procedure or obtained from the Msg3 buffer (operation2 e-15).

FIG. 2G is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 3 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2G, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 g-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 g-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 g-09).

Afterward, when the UE succeeds in the contention-free random access andthus receives an RAR message about the preamble, the UE determines thefollowing so as to transmit data on a UL resource assigned in the RARmessage:

In a case where the RAR message is not a first RAR successfully receivedin a random access procedure, and the UE determines that a size of a MACPDU stored in an Msg3 buffer is different from a size of UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 g-11), the UE indicates a multiplexing andassembly entity (that is, a different entity other than the Msg3 buffer)in the UE to re-generate a MAC PDU from a packet stored in the Msg3buffer, according to the size of the UL resource allocation received inthe RAR message (operation 2 g-13), and flushes (or deletes) the Msg3buffer (operation 2 g-17). When the UE indicates to re-generate the MACPDU from the packet stored in the Msg3 buffer, the UE may indicate tore-generate the MAC PDU by excluding some MAC subPDUs and including someMAC subPDUs from among MAC subPDUs that were to be transmitted from theMsg3 buffer. For example, the UE may indicate to re-generate the MAC PDUby including a handover completion RRC message. Also, the UE may add, tothe re-generated MAC PDU, a BSR MAC CE for reporting a buffer status soas to transmit UL data, but it is not necessary to include a MAC CE suchas the aforementioned C-RNTI MAC CE in the Msg3 that occurs after thecontention-free random access (because the BS already knows which UE hastransmitted the preamble), and thus the MAC CE such as theaforementioned C-RNTI MAC CE may be excluded. Also, depending onnecessity, the UE may include or may not include a PHR MAC CE forindicating remaining power for UL by the UE in the re-generated MAC PDU.

Afterward, the UE determines whether a packet is stored in the Msg3buffer. In a case where the UE flushes the Msg3 buffer in operation 2g-17 according to the aforementioned procedure, because the UE alreadyindicated the multiplexing and assembly entity to re-generate a packet,the UE obtains the MAC PDU from the entity and then transmits the MACPDU on the UL resource received in the RAR message (operation 2 g-19).Otherwise, the UE transmits the packet stored in the Msg3 buffer,without a change to the packet, on the UL resource received in the RARmessage (operation 2 g-21).

FIG. 2H is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 4 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2H, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 h-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 h-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 h-09).

Afterward, the UE succeeds in the contention-free random access anddetermines whether the UE receives an RAR message in response to thepreamble (operation 2 h-11).

When it is successful, as there is data in an Msg3 buffer which isstored during a previous contention-free random access, the UE obtains apacket from the Msg3 buffer so as to transmit it (operation 2 h-13).When the UE determines that a size of the obtained packet is differentfrom a size of UL resource allocation received in the RAR message (or,when the UE determines that the size of the UL resource allocationreceived in the RAR message is greater) (operation 2 h-15), the UEindicates a multiplexing and assembly entity (that is, a differententity other than the Msg3 buffer) in the UE to re-generate a MAC PDUfrom a packet stored in the Msg3 buffer, according to the size of the ULresource allocation received in the RAR message (operation 2 h-17).Alternatively, when transmission of the preamble is not selected fromamong contention-based random access preambles (i.e., selection of adedicated random access preamble) and the UE determines that the size ofthe obtained packet is different from the size of the UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 h-15), the UE may indicate the multiplexing andassembly entity (that is, the different entity other than the Msg3buffer) in the UE to re-generate the MAC PDU from a packet stored in theMsg3 buffer, according to the size of the UL resource allocationreceived in the RAR message (operation 2 h-17). When the UE indicates tore-generate the MAC PDU from the packet stored in the Msg3 buffer, theUE may indicate to re-generate the MAC PDU by excluding some MAC subPDUsand including some MAC subPDUs from among MAC subPDUs that were to betransmitted from the Msg3 buffer. For example, the UE may indicate tore-generate the MAC PDU by including a handover completion RRC message.Also, the UE may add, to the re-generated MAC PDU, a BSR MAC CE forreporting a buffer status so as to transmit UL data, but it is notnecessary to include a MAC CE such as the aforementioned C-RNTI MAC CEin the Msg3 that occurs after the contention-free random access (becausethe BS already knows which UE has transmitted the preamble), and thusthe MAC CE such as the aforementioned C-RNTI MAC CE may be excluded.Also, depending on necessity, the UE may include or may not include aPHR MAC CE for indicating remaining power for UL by the UE in there-generated MAC PDU.

Afterward, although the packet is stored in the Msg3 buffer, the UEobtains the data from the multiplexing and assembly entity and thentransmits the MAC PDU on the UL resource received in the RAR message(operation 2 h-19). Otherwise, the UE transmits the packet stored in theMsg3 buffer, without a change to the packet, on the UL resource receivedin the RAR message (operation 2 h-21).

FIG. 2I is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 5 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2I, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 i-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 i-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 i-09).

Afterward, when the UE succeeds in the contention-free random access andthus receives an RAR message about the preamble, the UE determines thefollowing so as to transmit data on a UL resource assigned in the RARmessage:

In a case where the RAR message is not a first RAR successfully receivedin a random access procedure, and the UE determines that a size of a MACPDU stored in an Msg3 buffer is different from a size of UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 i-11), the UE generates a MAC PDU by adding onlypadding (padding bits) to a packet in the existing Msg3 buffer so as tofit to the size of the UL resource allocation received in the RARmessage (operation 2 i-15), and stores the MAC PDU in the Msg3 buffer(operation 2 i-17).

Afterward, the UE determines whether a packet is stored in the Msg3buffer, and when the packet is stored, the UE transmits the packet inthe Msg3 buffer on the UL resource received in the RAR message(operation 2 i-19).

FIG. 2J is a diagram illustrating a procedure of operations of a UEaccording to Embodiment 6 of a method of generating and transmitting amessage3 when the UE performs a random access embodiments of thedisclosure. In descriptions below, the UE may be replaced with theaforementioned MAC entity.

Referring to FIG. 2J, a situation is assumed, in which the UE is in aconnected mode and first performs a contention-based random accessprocedure for handover as in the example of FIG. 2D (operation 2 j-03).When the random access fails, the UE determines whether SSB/CSI-RS towhich a dedicated random access preamble is assigned meets a conditionconfigured by a BS (operation 2 j-07), and when there are SSB/CSI-RSthat meet the condition, the UE selects one of the SSB/CSI-RS andperforms a contention-free random access by using a preamble assigned tothe corresponding SSB/CSI-RS (operation 2 j-09).

Afterward, the UE succeeds in the contention-free random access anddetermines whether the UE receives an RAR message in response to thepreamble (operation 2 j-11).

When it is successful, as there is data in an Msg3 buffer which isstored during a previous contention-free random access, the UE obtains apacket from the Msg3 buffer so as to transmit it (operation 2 j-13).When the UE determines that a size of the obtained packet is differentfrom a size of UL resource allocation received in the RAR message (or,when the UE determines that the size of the UL resource allocationreceived in the RAR message is greater) (operation 2 j-15), the UEre-generates a MAC PDU by adding only padding to a packet in theexisting Msg3 buffer so as to fit to the size of the UL resourceallocation received in the RAR message (operation 2 j-17).Alternatively, when transmission of the preamble is not selected fromamong contention-based random access preambles (i.e., selection of adedicated random access preamble) and the UE determines that the size ofthe obtained packet is different from the size of the UL resourceallocation received in the RAR message (or, when the UE determines thatthe size of the UL resource allocation received in the RAR message isgreater) (operation 2 j-15), the UE re-generates the MAC PDU by addingpadding according to the size of the UL resource allocation received inthe RAR message (operation 2 j-17).

Afterward, the UE transmits the packet (the MAC PDU) on the UL resourcereceived in the RAR message, the packet being re-generated according tothe aforementioned procedure or obtained from the Msg3 buffer (operation2 j-19).

That is, the UE according to some embodiments of the disclosure mayreport detailed information about a most-recent successful randomaccess, and in response thereto, the BS may appropriately allocate arandom access channel to UEs in a cell. Also, the afore-describedembodiments may each be implemented or may be implemented as acombination.

FIG. 2K illustrates a configuration of a UE in a wireless communicationsystem according to some embodiments of the disclosure.

Referring to FIG. 2K, the UE includes a RF processor 2 k-10, a basebandprocessor 2 k-20, a storage 2 k-30, and a controller 2 k-40. However,the UE is not limited thereto and may include more elements than theelements shown in FIG. 2K or may include less elements than the shownelements.

Furthermore, the UE in the wireless communication system of FIG. 2K maycorrespond to the configuration of the UE of FIG. 1H. For example, theRF processor 2 k-10 of FIG. 2K may correspond to the RF processor 1 h-10of FIG. 1H, and the baseband processor 2 k-20 of FIG. 2K may correspondto the baseband processor 1 h-20 of FIG. 1H. Also, the storage 2 k-30 ofFIG. 2K may correspond to the storage 1 h-30 of FIG. 1H, and thecontroller 2 k-40 of FIG. 2K may correspond to the controller 1 h-40 ofFIG. 1H.

The RF processor 2 k-10 may perform functions for transmitting andreceiving signals through radio channels, e.g., band conversion andamplification of the signals. That is, the RF processor 2 k-10 mayup-convert a baseband signal provided from the baseband processor 2k-20, into an RF band signal and then may transmit the RF band signalthrough an antenna, and may down-convert an RF band signal receivedthrough the antenna, into a baseband signal. For example, the RFprocessor 2 k-10 may include a transmit filter, a receive filter, anamplifier, a mixer, an oscillator, a DAC, an ADC, or the like. Althoughonly one antenna is illustrated in FIG. 2K, the UE may include aplurality of antennas. The RF processor 2 k-10 may include a pluralityof RF chains. The RF processor 2 k-10 may perform beamforming. Forbeamforming, the RF processor 2 k-10 may adjust phases and intensitiesof signals to be transmitted or received through a plurality of antennasor antenna elements. Also, the RF processor 2 k-10 may perform a MIMOoperation and may receive a plurality of layers in the MIMO operation.In response to the control by the controller 2 k-40, the RF processor 2k-10 may perform received beam sweeping by appropriately configuring aplurality of antennas or antenna elements, or may adjust a direction anda beam width of a received beam to coordinate with a transmit beam.

The baseband processor 2 k-20 may convert between a baseband signal anda bitstream based on physical entity specifications of a system. Forexample, for data transmission, the baseband processor 2 k-20 maygenerate complex symbols by encoding and modulating a transmitbitstream. For data reception, the baseband processor 2 k-20 mayreconstruct a received bitstream by demodulating and decoding a basebandsignal provided from the RF processor 2 k-10. For example, according toan OFDM scheme, for data transmission, the baseband processor 2 k-20 maygenerate complex symbols by encoding and modulating a transmitbitstream, may map the complex symbols to subcarriers, and then mayconfigure OFDM symbols by performing IFFT and CP insertion. For datareception, the baseband processor 2 k-20 may segment a baseband signalprovided from the RF processor 2 k-10, into OFDM symbol units, mayreconstruct signals mapped to subcarriers by performing FFT, and thenmay reconstruct a received bitstream by demodulating and decoding thesignals.

The baseband processor 2 k-20 and the RF processor 2 k-10 may transmitand receive signals as described above. Accordingly, the basebandprocessor 2 k-20 and the RF processor 2 k-10 may also be called atransmitter, a receiver, a transceiver, or a communicator. Also, atleast one of the baseband processor 2 k-20 and the RF processor 2 k-10may include a plurality of communication modules to support a pluralityof different radio access technologies. Also, at least one of thebaseband processor 2 k-20 and the RF processor 2 k-10 may includedifferent communication modules to process signals of differentfrequency bands. For example, the different radio access technologiesmay include a wireless LAN (e.g., IEEE 802.11), a cellular network(e.g., LTE), or the like. The different frequency bands may include aSHF (e.g., 2.5 GHz, 5 GHz) band and an mmWave (e.g., 60 GHz) band. TheUE may transmit and receive signals to and from the BS by using thebaseband processor 2 k-20 and the RF processor 2 k-10. In this regard,the signals may include control information and data.

The storage 2 k-30 may store basic programs, application programs, anddata, e.g., configuration information, for operations of the UE. Inparticular, the storage 2 k-30 may store information related to awireless LAN node that performs wireless communication by using awireless LAN access technology. Furthermore, the storage 2 k-30 mayprovide the stored data upon request by the controller 2 k-40. Thestorage 2 k-30 may include any or a combination of storage media such asROM, RAM, a hard disk, a CD-ROM, and a DVD. The storage 2 k-30 mayinclude a plurality of memories. According to some embodiments, thestorage 2 k-30 may store a program for performing the wirelesscommunication method for re-generating and transmitting data stored inan Msg3 buffer in the aforementioned random access procedure.

The controller 2 k-40 may control overall operations of the UE. Forexample, the controller 2 k-40 transmits and receives signals throughthe baseband processor 2 k-20 and the RF processor 2 k-10. Furthermore,the controller 2 k-40 records and reads data on or from the storage 2k-30. To this end, the controller 2 k-40 may include at least oneprocessor. For example, the controller 2 k-40 may include a CP forcontrolling communications and an AP for controlling an upper layer suchas an application program. According to some embodiments of thedisclosure, the controller 2 k-40 may include a multi-connectionprocessor 2 k-42 for processing operations of a multi-connection mode.For example, the controller 2 k-40 may control the UE to performillustrated processes in an operation of the UE which is described withreference to at least one of FIGS. 2E to 2J.

In a random access, the controller 2 k-40 according to some embodimentsof the disclosure determines whether a size of a packet in the Msg3buffer is different from a size of an UL resource received via a RAR,and when it is different, the controller 2 k-40 may generate Msg3according to the aforementioned embodiment and thus may transmit data onthe corresponding resource. Furthermore, at least one element in the UEmay be implemented as a chip.

The methods according to the embodiments of the disclosure as describedherein or in the following claims may be implemented as hardware,software, or a combination of hardware and software.

When implemented as software, a computer-readable storage medium storingone or more programs (e.g., software modules) may be provided. The oneor more programs stored in the computer-readable storage medium areconfigured for execution by one or more processors in an electronicdevice. The one or more programs include instructions directing theelectronic device to execute the methods according to the embodiments ofthe disclosure as described herein or in the following claims.

The programs (e.g., software modules or software) may be stored innon-volatile memory including RAM or flash memory, ROM, EEPROM, amagnetic disc storage device, a CD-ROM, a DVD, another optical storagedevice, or a magnetic cassette. Alternatively, the programs may bestored in memory including a combination of some or all of theabove-mentioned storage media. A plurality of such memories may beincluded.

In addition, the programs may be stored in an attachable storage deviceaccessible through any or a combination of communication networks suchas the Internet, an intranet, a LAN, a WLAN, and a SAN. Such a storagedevice may access, via an external port, the electronic device thatperforms embodiments of the disclosure. Furthermore, an additionalstorage device on the communication network may access the electronicdevice that performs embodiments of the disclosure.

In the afore-described embodiments of the disclosure, an element orelements included in the disclosure are expressed in a singular orplural form depending on the described embodiments of the disclosure.However, the singular or plural form is selected appropriately for asituation assumed for convenience of description, the disclosure is notlimited to the singular or plural form, and an element expressed in asingular form may include a plurality of elements and elements expressedin a plural form may include a single element.

Specific embodiments of the disclosure are described in the descriptionsof the disclosure, but it will be understood that various modificationsmay be made without departing the scope of the disclosure. Thus, thescope of the disclosure is not limited to the embodiments describedherein and should be defined by the appended claims and theirequivalents.

The invention claimed is:
 1. A method of performing a random accessprocedure, the method being performed by a user equipment (UE) andcomprising: selecting, from among a plurality of Synchronization SignalBlocks (SSBs), a first SSB that exceeds a threshold value of signalpower; transmitting a contention-based random access preamble in aPhysical Random Access Channel (PRACH) occasion corresponding to thefirst SSB; receiving a first Random Access Response (RAR) correspondingto the contention-based random access preamble; obtaining a first MediaAccess Control Protocol Data Unit (MAC PDU) corresponding to a size ofuplink (UL) resource allocation in the first RAR; transmitting amessage3 (Msg3) comprising the first MAC PDU; determining, based on areception of a response to the Msg3, whether contention is resolved; andin case that the contention is not resolved, performing acontention-free random access procedure, wherein the performing of thecontention-free random access procedure comprises: selecting a secondSSB exceeding the threshold value of the signal power, from among aplurality of SSBs with which contention-free random access preambles areassociated; transmitting a contention-free random access preamblecorresponding to the second SSB; receiving a second RAR corresponding tothe contention-free random access preamble; in case that a size of ULresource allocation in the second RAR does not match with a size of thefirst MAC PDU, obtaining a second MAC PDU including at least one MACsubProtocol Data Unit (MAC subPDU) the at least one MAC subPDU includinga handover completion Radio Resource Control (RRC) message in the firstMAC PDU; and transmitting the second MAC PDU.
 2. The method of claim 1,wherein the first MAC PDU is obtained from a multiplexing and assemblyentity.
 3. The method of claim 1, wherein the first MAC PDU comprises aCell-Radio Network Temporary Identifier Media Access Control ControlElement (C-RNTI MAC CE).
 4. The method of claim 1, further comprisingstoring the first MAC PDU in an Msg3 buffer.
 5. The method of claim 1,wherein the obtaining of the first MAC PDU comprises: determiningwhether the first MAC PDU is stored in an Msg3 buffer; and based on aresult of the determining, obtaining the first MAC PDU from the Msg3buffer.
 6. The method of claim 1, wherein the second MAC PDU is obtainedfrom a multiplexing and assembly entity.
 7. The method of claim 5,further comprising deleting the first MAC PDU in the Msg3 buffer.
 8. Themethod of claim 1, wherein the determining of whether the contention isresolved comprises determining whether the response to the Msg3 isreceived until a ra-ContentionResolution timer is expired.
 9. A userequipment (UE) performing a random access procedure, the UE comprising:a transceiver; and at least one controller coupled with the transceiverand configured to: select, from among a plurality of SynchronizationSignal Blocks (SSBs), a first SSB that exceeds a threshold value ofsignal power, transmit a contention-based random access preamble in aPhysical Random Access Channel (PRACH) occasion corresponding to thefirst SSB, receive a first Random Access Response (RAR) corresponding tothe contention-based random access preamble, obtain a first Media AccessControl Protocol Data Unit (MAC PDU) corresponding to a size of uplink(UL) resource allocation in the first RAR, transmit a message3 (Msg3)comprising the first MAC PDU, determine, based on a reception of aresponse to the Msg3, whether contention is resolved, and in case thatthe contention is not resolved, perform a contention-free random accessprocedure, wherein the performing of the contention-free random accessprocedure comprises that the at least one controller is furtherconfigured to: select a second SSB exceeding the threshold value of thesignal power, from among a plurality of SSBs with which contention-freerandom access preambles are associated, transmit a contention-freerandom access preamble corresponding to the second SSB, receive a secondRAR corresponding to the contention-free random access preamble, in casethat a size of UL resource allocation in the second RAR does not matchwith a size of the first MAC PDU, obtain a second MAC PDU including atleast one MAC subProtocol Data Unit (MAC subPDU) the at least one MACsubPDU including a handover completion Radio Resource Control (RRC)message in the first MAC PDU, and transmit the second MAC PDU.
 10. TheUE of claim 9, wherein the at least one controller is further configuredto determine whether the first MAC PDU is stored in an Msg3 buffer, andbased on a result of the determining, obtain the first MAC PDU from theMsg3 buffer.
 11. The UE of claim 9, wherein the second MAC PDU isobtained from a multiplexing and assembly entity.
 12. The UE of claim10, wherein the at least one controller is further configured to deletethe first MAC PDU in the Msg3 buffer.